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The study investigated the dependences of the structural, magnetic, and optical properties of double manganites NdBaMn2O6 on the degree of order of Nd and Ba atoms in the A-position. Analysis of the temperature dependences of light transmission showed the changes of the charge carrier subsystem in the region of structural and magnetic phase transitions. If there was a metal–insulator transition, the magnetotransmission near the Curie temperature was detected. [ABSTRACT FROM AUTHOR]

Structural, magnetic and optical properties of double manganites PrBaMn2O6 and NdBaMn2O6 are studied depending on the degree of ordering in the A-position. It is shown that, annealing induced disordering goes in an initial stage throw formation of a two-phase state: a phase with a high A-site ordering with TC ∼ 280–300 K and a phase with a low ordering of ~30% with significantly lower TC coexist. In partially ordered PrBaMn2O6 samples there are metal-insulator transitions near TC of the each coexisting phases. In partially ordered NdBaMn2O6 in a highly A-site ordered high-temperature phase, there is no metal-insulator transition due to the destruction of the channels for metallic conductivity formed by the ordering of the x2‒y2 orbitals. If a metal-insulator transition takes place, the application of a magnetic field leads to the effect of magnetotransmission near TC, which is associated with a change in the concentration of delocalized charge carriers. [ABSTRACT FROM AUTHOR]

Components of event-related potentials (ERP) were studied using an active sound signal discrimination task in northern schoolchildren aged 12-18 years with impaired mental development and learning difficulties (IQ 65 ± 4) and without mental developmental impairments (IQ 90 ± 10). The peak latency of the P300 component in the central and parietal areas of the cortex on perception and discrimination of target sound stimuli was greater in northern children with impaired mental development (Cz 370 ± 36 msec, 8.8 ± 4.1 μV; Pz 375 ± 39 msec, 10.2 ± 3.3 μV) as compared with their normally developing peers (339 ± 28 msec, 10.4 ± 3.0 μV; 340 ± 35 msec, 12.2 ± 2.2 μV, respectively). Negative correlations were found between cognitive abilities, the accuracy and speed of information processing in an attention task, and the latency of the P300 component, with positive correlations with the amplitude of the P3 component for measures of attention. The spatial, temporal, and amplitude characteristics of ERP in adolescents with impaired mental development reflect the functional incompetence or immaturity of the hierarchical organization of the system processing and discriminating information arriving in the brain and requiring concentration of attention and decision-taking. [ABSTRACT FROM AUTHOR]

The effects of sharp variations in geomagnetic and solar activity at high latitudes on human brain bioelectrical activity were studied using a multichannel EEG structural function. Studies were performed on 10 healthy men aged 19-37 years. EEG recordings were made daily for 25 days. Solar flares of classes C and M occurred during the study period, as did geomagnetic storms of levels G2-G3. A first-order temporal structural function (SF) in eight-dimensional space was calculated from the EEG. The time scales of internal correlations in the multichannel EEG were assessed using the radius of the correlation of the SF, while the spatial correlational structure of the EEG was assessed in terms of the SF asymptote. Variations in geomagnetic activity were found to be reflected more in changes in the correlation radius than the level of the SF asymptote. Perturbing and modulating effects of geomagnetic and solar activity on SF parameters and the SF spectrum were identified. Thus, the SF of the multichannel EEG can be used to evaluate the integral reaction of the brain as a unified system to the actions of heliogeophysical factors and can be used in studies of the effects of the environment on humans. [ABSTRACT FROM AUTHOR]

Powder and single-crystal samples of the high-temperature superconductor Bi2Sr2CaCu2O8 + x are studied by X-ray diffraction. Its thermal expansion coefficient is found to be negative over a wide temperature range (160–260 K). Possible causes of this effect are discussed. [ABSTRACT FROM AUTHOR]

Powder and single-crystal samples of the high-temperature superconductor Bi2Sr2CaCu2O8 + x are studied by X-ray diffraction. Its thermal expansion coefficient is found to be negative over a wide temperature range (160–260 K). Possible causes of this effect are discussed. [ABSTRACT FROM AUTHOR]