Association between cold stress and oxidative stress was demonstrated by measuring the activity of two antioxidant enzymes and the level of free radicals generated in two batches of cells of an Antarctic bacterium Pseudomonas fluorescens MTCC 667, grown at 22 and 4°C. Increase in oxidative stress in cells grown at low temperature was evidenced by increase in the activity of an enzyme and also in the amount of free radicals generated, in the cold-grown cells. The association between cold stress and oxidative stress demonstrated in this investigation bolsters the concept of interlinked stress response in bacteria.

The effects of Gd addition on the phase evolution and superconducting properties of (Bi, Pb)-2212 prepared in the bulk polycrystalline form were studied. The Gd content in the samples was varied from 0.0 to 0.5 on a general stoichiometry of Bi1.7Pb0.4Sr2.0Ca1.1Cu2.1GdxOy. Phase analysis by means of x-ray diffraction, microstructural examination by scanning electron microscopy and superconducting property studies were carried out to evaluate the relative performances of the samples. It is observed that Gd addition enhances the transition temperature (TC) and critical current density (JC) of the system. Moreover no secondary phase containing Gd ions or any other cations was observed after the final stage of heat treatment. Microstructural examination shows clear and distinct morphologies for the Gd-added samples, wherein the grain growth is suppressed by the addition of Gd and the edges of the grains become more and more rounded. As a result, there is an increase in the porosity of the Gd-added samples, leading to a reduction in the sintered density for these samples.

The critical current density and flux pinning properties of Bi1.6Pb0.5Sr2−xEuxCa1.1Cu2.1Oy (where x = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) prepared by solid state synthesis in bulk polycrystalline form were studied. The samples were characterized by powder x-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy-dispersive x-ray analysis (EDS) and superconductivity measurements. The critical temperature (TC), critical current density (JC) and field dependence of JC of the Eu-substituted samples were found to be highly enhanced for optimum doping levels. The peak position of the normalized pinning force density (Fp/Fpmax) is found to shift to higher fields (0.88 T) for optimally doped samples in contrast to 0.2 T for the undoped sample. The enhancement of the JC–B characteristic and pinning force density FP (FP = JC × B) due to Eu substitution is of great technological significance.

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