John Walberg Anderson

Isolation of synaptic complexes in a caesium chloride density gradient: electron microscopic and immunohistochemical studies.

A technique is described for the improved isolation of synaptic complexes. Homogenates of guinea pig cerebellum and cerebral cortex were subjected to centrifugation, first in a discontinuous sucrose gradient, and secondly in a continuous caesium chloride gradient. Of the six bands that were obtained, band four contained a high proportion of synaptic complexes showing both pre‐ and postsynaptic elements attached to each other; myelin and free mitochondria were not contaminants of this fraction. Fluorescein‐labelled γ‐globulin prepared against band four reacted with synaptic regions of cerebellum and cerebral cortex, but not with cervical cord.

The effect of lead content on the critical current density, irreversibility field, and microstructure of Ag-clad Bi 1.8 Pb x Sr 2 Ca 2 Cu 3 O y tapes

We studied the effect of lead content ( x = 0.20−0.40) on the critical current density J c (0 T, 77 K), irreversibility field H * (77 K), and microstructure of monocore, Ag-clad Bi 1.8 Pb x Sr 2 Ca 2 Cu 3 O y (2223) tapes, finding that tapes with lower lead contents ( x = 0.20–0.25) required higher processing temperatures (840 and 832 °C, respectively) to complete 2223 formation, as compared to the optimum 820 °C reaction temperature of the x = 0.30–0.40 tapes. We found that both the zero-field and the in-field properties correlated strongly to the phase purity with J c (0 T, 77 K) reaching a maximum of ˜20 kA/cm 2 for x = 0.30, and then decreasing with increasing lead content to ˜12 kA/cm 2 for x = 0.40. H * (77 K) increased from ˜165 mT at x = 0.20 to ˜265 mT at x = 0.30, then declined to 195 mT at x = 0.40. Optimizing the lead content at x = 0.30 maximized both the connectivity and the flux pinning contributions to the critical current density.

Determination of irreversibility field variations in mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox tapes by transport current methods

The irreversibility field, H*, has been measured for a variety of mono- and multifilamentary (Bi,Pb)2Sr2Ca2Cu3Ox (2223) tapes using two different transport current techniques. It is common to characterize the quality of 2223 tapes by their zero-field, 77 K critical current density [Jc(0 T, 77 K)], even though this ignores the fact that significant self-fields depress Jc(0 T, 77 K) and the possibility that the in-field Jc(B) characteristics may be optimized independently of the Jc(0 T, 77 K) value. To provide more useful information, we propose a second characterization, that of the irreversibility field, H*. Having both H* and Jc(0 T, 77 K) information helps in separating the two independent contributions that better connectivity and stronger flux pinning can make to the Jc of a tape. We illustrate this point with results from a variety of mono- and multifilamentary Bi-2223/Ag tapes in damaged and undamaged conditions, which show that H* (77 K) can vary from ∼100 to ∼200 mT and not directly correlate with...

The effect of wire drawing and cold rolling on the precursor 2212 phase texture and its subsequent influence on the (Bi,Pb)/sub 2/Sr/sub 2/Ca/sub 2/Cu/sub 3/O/sub x/ texture in Ag-clad tapes

We have studied the effect of wire drawing and cold rolling on the texture development of precursor (Bi,Pb)₂Sr₂CaCu₂0_x (2212) phase and its influence on the subsequent (Bi,Pb)₂Sr₂Ca₂Cu₃0_y (2223) phase texture in Ag-clad tapes. A mixture of (Bi,Pb)₂Cu0₄ and SrCaCu0₃ powders having an overall 2223 composition was reacted to form the 2212 phase at different stages of deformation. X-ray diffraction peak height analysis was used to quantify the 2212 texture F₂₂₁₂= I(OOS)/[I(OO8)+I(115)] at various oxide filament thickness. Wires containing powder reacted to the 2212 phase prior to loading into a Ag tube had F<sub>2212≈0.3 after drawing. This texture increased to F₂₂₁₂=0.7 upon rolling. Two other composites reacted to the 2212 phase immediately after drawing, and after being drawn and partially rolled, had worse initial textures, but improved during rolling to FzZl2≈0.7. Samples reacted to 2212 after rolling was complete had F₂₂₁₂≈0.35. The results indicate that the 2212 texture reaches a maximum value of F₂₂₁₂≈0.7 and remains at that level upon subsequent rolling. Samples of filament thickness ≈80 μm were then reacted to form 2223. For the samples which contained 2212 that had received at least some mechanical deformation, the 2223 phase formed with a texture factor F₂₂₂₃ > 0.9, while the tape that contained 2212 formed after rolling developed a 2223 texture of only F₂₂₂₃≈0.75. The results show that there is a substantial texture enhancement upon reaction to 2223, which could be the result of either the 2223 formation mechanism or geometrically constrained grain growth.