We fabricated screen-printed Ag-(Bi,Pb)2Sr2Ca2Cu3Ox monofilament and multifilament tapes with filament number 1≤N≤5. As N increases, the critical current Ic increases monotonically until it reaches 54 A (77 K, 0 T) for N=5, while the critical current density Jc is around 1.6×104 A/cm2 (77 K, 0 T) nearly independent of N. The bend strain tolerance is found to decrease with increasing N. For monofilament tapes the strain tolerance is 2%–3% strain while for multifilament tapes it decreases to ∼1% at N=3 and ∼0.4% at N=5.
A process of combined rolling and uniaxial pressing with intermediate sintering steps for fabrication of screen-printed (Bi,Pb)2Sr2Ca2Cu3Ox thick films sandwiched between Ag substrates yields c-axis-oriented microstructures with a high critical current density (Jc) of 1.5×104 A/cm2 (77 K, 0 T) and 9.0×104 A/cm2 (23 K, 0 T). The measured Jc anisotropy at 77 K, as a function of the angle θ between B and c axis, is pronounced. An increase in B sharpens a peak at θ=90° (i.e., B⊥c) in the Jc vs θ curve, together with enhancement of the anisotropy ratio defined as Jc(B⊥c)/Jc(B∥c). In high fields above 0.5 T, the half-height angular width of the peak approaches an average misalignment angle (4°–6°) between the grains with increasing B.
SUMMARYWe study the applicability and evaluate the decryption fidelity of a spread spectrum image encryption method, for which decryption is accomplishedwith easy operations, and which makes possible the protection of secrecy even in hardcopy form. Decryption in the spread spectrum encryption method is based on the recognition of the dark-pixel region in the picture's background noise. To evaluate the applicability of this image encryption method, we employ measure B,,, called the boldfacedness, which estimates the boldness of the original image. This is essentially the area of the dark-pixel region normalized by the length of the path surrounding it. We relate the intuitivevisibilityof several kinds of images to the boldfacedness, and confirm its validity. To estimate its applicability, we composed a questionnaire concerning the recognition of simple rectangular images in background noise. The results showed that for these simple rectangular images a B,, value down to about 0.023 is adequate. Next, since we often want to transmit images of documents in facsimile, we evaluated the fidelity of document images based on the size and type of several kinds of characters. To perform this evaluation we took as input Group 3 facsimile, with the resolution of all document images as a consistent 200 dpi. It became clear that, for document images, the letter-recognition threshold value of B,, is in the neighborhood of 0.015. This is equivalent to the case both for 16-point Mincho-tai characters and for 10-point standard characters, verifying the applicabilityof this encryption method for general document usage.Key words: Spread spectrum encryption methods, image boldfacedness; accuracy of the decrypted image.
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