• HTc bulk superconductors – precursors, technologic procedures, measuring methods and properties
• Statistical methods for interval estimators for a variance component
• Magnetometric method of investigation of the relaxation of ferromagnetic micro-particles dispersed in medium approximating the intracellular environment

Result 1: HTc bulk superconductors – precursors, technologic procedures, measuring methods and properties

Projects: VEGA 2/4091/04 a 2/7083/27

Investigators: A. Cigáň, J. Maňka, M. Kopčok, F. Hanic, K. Jurča

We have investigated the scandium doped YBa₂Cu₃O_y - Sc₂O₃ system, which a little attention is paid to at present. The samples were prepared by solid state reaction from stoichiometric mixtures of oxides and BaCO₃ with a nominal composition of YBa₂(Cu_3-xSc_x)O_y. The investigated range of x was from 0 to 1.2. The superconducting phase is manifested up to x = 1.0. The Sc doping affects the critical temperature T_c and the transition width ΔT_c only slightly, unlike the volume magnetization and microstructure. In addition to the superconducting phase, there is main excess nonsuperconducting phase(s) starting from x = 0.30, which could belong to the family of paramagnetic Ba₃Cu₃Sc₄O₁₂ phase. The solubility limit of Sc in solid solution of YBa₂(Cu_3-xSc_x)O_y is about x = 0.15. The superconducting phases are present up to nominal x = 1.0. Their T_c and ΔT_c change only slightly with Sc doping, at x = 0.9 they are still 87.4 K and 1.9 K, respectively.

Figure: Comparison of the magnetization curves of typical sintered samples doped by 0, 10 and 33 % of scandium. With increasing scandium level the magnetization of samples decreases.

Publication:

Result 2: Statistical methods for interval estimators for a variance component

Project: APVV RPEU-0008-06; VEGA 1/3016/06

Investigator: B. Arendacká

Suggested was a new alternative construction for a specific interval and comparison of confidence intervals for a variance component corresponding to the random factor in mixed linear models with two variance components was carried out. We showed that the interval originally proposed by El-Bassiouni (Communications in Statistics, 1994), and recommended solely on the basis of simulation results, has theoretically guaranteed the required probability of coverage in certain limiting situations. In general, there exists a theoretical lower bound for its probability of coverage, which follows from the fact that, as we showed, this interval can be derived by a method suggested by Williams (Biometrika, 1952). In view of the stated findings, El-Bassiouni's interval can be regarded as a standard that new confidence intervals obtained by generalized inference approach can be compared with. Simulation results confirmed good performance of El-Bassiouni's interval and revealed which generalized confidence intervals are comparable with it. Also, mutual relations between the different generalized confidence intervals were pointed out.

Figure: The figure illustrates construction of an approximate confidence interval for a variance component in linear models with random effects by Williams' method.

Publications:

Result 3: Magnetometric method of investigation of the relaxation of ferromagnetic micro-particles dispersed in medium approximating the intracellular environment

Projects: APVV-51-059005 a VEGA 2/7084/27

Investigators: J.Maňka, I .Šimáček, P. Jurdák, M. Škrátek

Relaxation is an accompanying effect occurring after magnetization of the ferromagnetic substances in biological objects. The living organism changes the orientation of vectors of magnetic moments of the ferromagnetic microparticles (FMC) in time, which decreases the total level of measured magnetic signal. The most part of FMC motion happens in the intracellular medium, e.g. in the alveolar macrophages, or hepatal proteins, such as hemosiderine or feritine. As mostly it is a problem to extract these biological complexes from the living organism, we have performed a series of measurements of magnetized FMC of Fe₃O₄ in media which model in vitro relaxation process in the intracellular environment. We have performed measurements of the relaxation characteristics on series of ferro- and ferrimagnetic powder samples (Fe₃O₄ and γ-Fe₂O₃) dispersed in the diamagnetic epoxy 371 with the viscosity η = 20 Pa.s or in dimetylpolysiloxan with η = 0.2 Pa.s. for three levels of the magnetization field (6, 30 and 120 mT). Theoretical analysis showed that besides the viscosity and external magnetic fields influence it is necessary to consider also the interaction among the FMC. Obtained results will be applied in modeling of the magnetic substances relaxation in the environment of living cells and structures and used for correction of the data in biomagnetometric measurements of the living organisms. The result has been obtained in cooperation with the Faculty of Medicine, Comenius University in Bratislava.

Publication:

• JURDÁK, Peter - KOPÁNI, M. - ŠIMÁČEK, Ivan – MAŇKA, Ján – ŠKRÁTEK, Martin. Magnetometric measurements of ferromagnetic micro-particles dispersed in medium approximating the intracellular environment. In 2007 MRS Fall Meeting. Boston, MA, November 26-30, 2007. Poster.