[en] Responses of pigmented pathogenic fungi and E. coli strains differing in DNA repair and catalase proficiency to direct and indirect effects of ultraviolet radiation were evaluated. Pigments in the four fungal pathogens of Citrus differed in their ability to protect against direct UV and damage by UV-A -mediated phototoxins of both host and non-host origin. UV-A and UV-B did not inactivate the fungal species. Differential protection in wild type strains of the two Fusarium spp. and in the wild type strains of the two Penicilium spp. against UV-C was observed. Wild type and mutants with altered coloration in Penicilium spp. protected to varying extent against both α-T and 8-MOP in the presence of UV-A. UV-B irradiation of E. coli resulted in inactivation of strains deficient in DNA excision repair. Plasmid DNA damaged in vitro by UV-B from lamp systems as well as by sunlight, and transformed in vivo into bacterial cells lacking specific nucleases showed reduced transformation in DNA excision repair strains. UV-B enriched wavelengths isolated from a solar simulator affected plasmid DNA in a similar manner as UV-B from lamp systems. Sunlight, however affected the membrane of whole cells. Concentration of foliar furanocoumarins of Citrus jambhiri decreased with UV-B irradiation. Phototoxicity to Fusarium spp. was accounted for, in part, by furanocoumarins, psoralen and bergapten (5-MOP) and others. Pure psoralen and 5-MOP affected both Fusarium spp. similarly and carotenoids protected only partially in the wild type strains. Citrus targetted the cell membrane in Fusarium spp.l and in E. coli strains; carotenoids in both of which protected against such damage. Loss in structural integrity of plasmid DNA when treated with citral and UV-A correlated with loss in transforming activity. Biological damage to membrane and DNA was due to the production of hydrogen peroxide. Fruit-rot pathogens Penicilium spp. were not affected by either furanocoumarins or citrals

[en] Materials in the Bi-Ca-Sr-Cu-O system were prepared by melt-quenching, followed by crystallization at elevated temperatures. Emphasis was placed on determining the processing conditions for the growth of textured 2223 grains by heat-treatment in thermal gradients. Results are reported for compositions doped with Pb and Sb. Heat-treatments in an atmosphere containing 10 percent O2 (and 90 percent Ar), and in small thermal gradients (2-6 C/cm), promoted the formation of oriented microstructures with good superconducting properties. The resistance-temperature characteristics were found to depend on the oxygen content in the heat-treatment atmosphere, and on the magnitude of the thermal gradient. The best specimens had sharp resistance transitions with zero resistance near 110 K. Experimental results are discussed in the context of phase development and ceramic microstructure. Emphasis is placed on the evolution of superconducting properties with heat-treatment conditions. 13 refs

[en] Single crystals of Y_1-xPr_xBa₂Cu₃O_7-δ (x = 0 ∼ 1) and Bi₂Sr₂CaCu₂O₈ were grown by flux methods. The morphology of the crystals was characterized by OM, SEM, XRD and TEM. This investigation focuses on the role of planar defects, such as twins and intergrowths, on superconducting properties. Property measurements were carried out by electrical and diamagnetic methods. Growth conditions are discussed in the context of defect formation, growth habit and morphology

[en] A systematic study was carried out on the crystal growth of superconductors in the series (BiO)₂Ca_n-1Sr₂Cu_nO_2n+2. (n=1, 2, 3). Centimeter size crystals of 2021 (n=1) and 2122 (n=2) were grown by a flux method, but only millimeter size crystals of 2223 (n=3) could be obtained by crystallization from the solid state. The extremely anisotropic growth habit impeded the development of thicker single crystals (thickness > 100μ). A strong correlation between starting composition, intergrowth content, and superconducting properties was determined. Syntactic intergrowths and large-are growth twins with a (110) coherent twin boundary and (001) composition plane were identified by OM, SEM, TEM and XRD. Details of twin morphology and structure are presented in the context of twin formation and growth. Superconducting properties for the twinned crystals were determined by magnetic and electrical measurements. The results indicate that growth steps, and not twin boundaries, significantly affect the resistance-temperature characteristics of the crystals

[en] Three superconducting phases in the Bi-Sr-Ca-Cu-O system have been discovered. In this investigation, emphasis was placed on optimizing conditions for the directional growth of the high T_c phase (2223, with a T_c ∼ 107K). A systematic study of factors favorable for the promotion of the high T_c phase (e.g., starting composition, chemical modification, heat-treatment, etc.) was carried out. Small amounts of Pb and Sb additives, coupled with heat-treatment in reduced oxygen atmospheres, resulted in a significant improvement in properties. Development of the high T_c phase will be discussed with respect to XRD, SEM, TEM, SQUID, and resistivity data. The use of thermal gradients (stationary and moving zones) as well as mechanical methods (rolling, swaging) will be discussed in the context of grain alignment and critical current densities

[en] Short communication. 4 refs

[en] Three superconducting phases in the system Bi-Ca-Sr-Cu-O have been discovered. To date, the high T_c phase (2223, with a T_c ∼ 107 K) has not been isolated in pure form. In this investigation, emphasis was placed on optimizing conditions for the growth of the high T_c phase. Melt-quenching and plasma spray methods were utilized to selectively promote the 2223 phase. A systematic study of factors favorable for the promotion of the high T_c phase (e.g., starting composition, chemical modification, het-treatment, etc.) was carried out. Small amounts of Pb and Sb additives, coupled with heat-treatment in reduced oxygen atmospheres, resulted in a significant improvement in properties. Development of the high T_c phase will be discussed with respect to XRD, SEM, TEM, SQUID, and resistivity data. The use of a moving-zone method and heat-treatment in a thermal gradient will be discussed in the context of grain alignment and critical current densities

[en] Superconductors in the system Bi-Ca-Sr-Cu-O were prepared from mixtures with initial cation proportions of 1111 and 6356. The effects of heat-treatment conditions, particularly, temperature, atmosphere, and cooling rates, on diamagnetic transition characteristics, were investigated. Calcined powders were found to be comprised primarily of the '2122 phase'. The transition temperature associated with this phase was determined to range from 60-80 K, depending upon the thermal processing conditions. By contrast with YBa₂Cu₃O_7-δ, the superconducting transition temperature T_c, was found to (i) decrease on annealing in oxygen and (ii) increase with increasing cooling rate in air. The increase in T_c observed for rapid cooling and quenching was related to an oxygen deficiency effect rather than to the cooling rate per se. An additional phase associated with a higher transition temperature of 112 K was present in all samples. The Meissner effect for this secondary phase was greatest for powder calcined at temperatures lower than the optimum conditions for the formation of the 2122 phase. The T_c for the second phase was found to be independent of the thermal processing conditions. 9 refs

[en] Oxide materials in the Bi-Ca-Sr-Cu system were prepared by a melt-quench method. The starting compositions were 2-2-2-3, 2-3-2-4 and 2-4-2-5. Three superconducting phases, 2-0-2-1, 2-1-2-2 and 2-2-2-3, crystallized sequentially in specific heat-treatment regimes. The phases corresponded to the single-, double-, and triple-layered structures with T_c values of 20, 80 and 105 K respectively. The high-T_c phase developed after prolonged heat treatment at 865 deg.C. Superconducting transitions as high as 105 K were observed. The results suggest that an interaction between an unidentified liquid phase and 2-1-2-2 promotes the development of the 2-2-2-3 phase. 21 refs.; 7 figs.; 1 table

[en] Superconducting coatings in the system Bi-Ca-Sr-Cu-O were deposited on alumina substrates by plasma spray methods. The coatings were superconducting in the ''as-sprayed'' condition and improved with heat treatment. The best results were for coatings with resistivity values near 10 mΩ cm at room temperature and zero resistance at 96 K. The coatings had a magnetic transition near 80 K, with a weak diamagnetic signal up to 112 K. Superconductivity in the coatings was associated with two distinct phases, one of which was not identified. Scanning electron microscopy, x-ray diffraction, electrical resistivity, and magnetic measurements were used to characterize the coatings