Browsing by Author "Terzieva S."

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    Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics
    (2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.
    We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.
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    Phase formation and microstructure in Re1-xCax Ba2Cu3Oz (Re=Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics
    (2006-03-01) Stoyanova-Ivanova A.; Terzieva S.; Staneva A.; Mikli V.; Traksmaa R.; Dimitriev Y.; Kovachev V.
    We have investigated the influence of Ca-substitution and different rare earths on the microstructure of RE1-xCax Ba2Cu3O7-δ (RE= Y, Eu, Er; x=0, 0.2, 0.3) superconducting ceramics. Scanning electron microscopy, X-ray microanalysis and energy dispersive spectroscopy have been used to study the microstructure and the chemical composition of the samples. A correlation was established between the polycrystalline microstructure and phase formation depending on the additive content. We observed that calcium is distributed uniformly in the crystals. The formation of minor impurity phases improved the sintering conditions. © Central European Science Journals Warsaw and Springer-Verlag Berlin Heidelberg 2006.
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    Student-centered learning in a bilingual environment - A possible approach to achieve specific goals in engineering education
    (2018-01-01) Kolarski V.; Danalev D.; Terzieva S.
    The educational approach to student-centered learning (SCL) is applied to develop engineering and communicative skills of students studying biotechnology. A new educational model has been developed. It is based on: students' needs reporting, use of authentic professional tasks and materials in a bilingual form; collaboration and team work, learning activities that reflect the professional duties of specialists in their workplace; specific achievement assessment (academic knowledge, skills and communicative competencies).
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    Synthesis and superconducting properties of Nd0.33 Eu0.08Gd0.58Ba2Cu3 Oz materials
    (2008-03-01) Stoyanova-Ivanova A.; Terzieva S.; Shivachev B.; Mikli V.; Vladimirova L.
    We have studied the effect of the ratio of different rare-earth element on the superconducting properties and phase formation of (Nd0.33Eu0.08Gd0.58)Ba2 Cu3Oz ceramic. Bulk NEG samples were prepared using the solid-state reaction process. The superconducting transition for Nd0.33Eu0.08Gd0.58Ba2 Cu3Oz is Tc ≈ 90 K and the value of the critical current density (Jc) is 13.9 A/cm2 at 77 K under zero magnetic fields. This value is twice as high when compared with the (Jc) value of YBCO systems (J3 = 7.31 A/cm2). The obtained bulk sample was used for the production of superconducting Ag-sheathed tapes by OPIT method including hot rolling. The critical current density of the obtained tape (337 A/cm2) is one order higher than the one of the bulk sample. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2008.