Band structure of (Sr3Sc2O5)Fe2As2 as a possible parent phase for new FeAs superconductors

By means of first-principles FLAPW-GGA calculations, we have investigated the electronic properties of the newly synthesized layered phase - (Sr3Sc2O5)Fe2As2. The electronic bands, density of states and Fermi surface have been evaluated. The resembling of our data for (Sr3Sc2O5)Fe2As2 with band structure pictures of known FeAs superconducting materials may be considered as the theoretical background specifying the possibility for (Sr3Sc2O5)Fe2As2 to become a parent phase for new FeAs superconductors.Comment: 10 pages, 4 figures, 3 table

Investigation of industrial compositions SONKOR as corrosion inhibitors of mild steel in neutral media containing hydrogen sulfide

Electrochemical and corrosion behavior of mild steel in neutral media containing hydrogen sulfide has been investigated by weight-loss and electrochemical methods and protective effect of industrial compositions SONKOR has been determined. It has been shown that in 3 % NaCl compositions SONKOR have weak protective effect but it increases greatly in presence of hydrogen sulfide in the solution. At concentration of H2S = 0,6 gram per liter maximal protective effect has SONKOR 9801 (85.57 %) and SONKOR 9920А (81.97 %). Inhibitors SONKOR 9021С (70.82 %), 9510А (73.11 %) и 9701 (67.87 %) show less protective effect

Band structure of SrFeAsF and CaFeAsF as parent phases for a new group of oxygen-free FeAs superconductors

By means of first-principle FLAPW-GGA calculations, we have investigated the electronic properties of the newly discovered layered quaternary systems SrFeAsF and CaFeAsF as parent phases for a new group of oxygen-free FeAs superconductors. The electronic bands, density of states, Fermi surfaces, atomic charges, together with Sommerfeld coefficients and molar Pauli paramagnetic susceptibility have been evaluated and discussed in comparison with oxyarsenide LaFeAsO - a parent phase for a new class of high-temperature (Tc about 26-56K) oxygen-containing FeAs superconductors. Similarity of our data for SrFeAsF and CaFeAsF with the band structure of oxygen-containing FeAs superconducting materials may be considered as theoretical background specifying the possibility of superconductivity in these oxygen-free systems.Comment: 12 pages, 3 figure

The influence of various factors on recovery process of motor control of paretic limbs muscles in patients with pyramidal syndrome

In order to study the specific features of central nervous system reaction to restoration of the cranial vault bone defects by distraction, osteosynthesis method, the electroneuromyographic examination was performed in 28 patients of 16—62 years (average age — 40,1 ± 2,6 years) with pyramidal syndrome in late recovery or residual period, of the disease (severe brain injury cerebral stroke). The main trends in electroneuromyographic indice — "cerebrospinal index" — in patients during the replacement process of post-traumatic or simulated cranial vault bone defects using transosseous distraction osteosynthesis were analyzed. The specific features of the central nervous system responses to surgical treatment, age, etiology, the brain structures initial lesion severity and disease duration were studied. As the results of the research it was established that replacement of defects of calvarium bones by transosseous distraction osteosynthesis in patients with consequences of craniocerebral trauma or stroke had. more intensive positive influence on motor zones of cerebral cortex, that shows itself in increase of effectiveness of motor control, in middle age people, at traumatic etiology of disease, at moderate pyramidal insufficiency and. at remoteness of the disease up to 1 year. Obtained data is expedient to take into account at primary selection of patients for operative treatment

BILATERAL INTERRELATIONS OF ENMGAND EEG-CHARACTERISTICS OF PYRAMID INSUFFICIENCY IN PATIENTS WITH THE CONSEQUENCES OF STROKE AND OF BRAIN INJURY

The aim. of the work was to estimate the degree of intensity of interhemispheric interaction with use of complex neurophysiological (electroneuromyography, electroencephalography) testing of 163 patients of 12—74 years in residual period, of ischemic (n = 108) and hemorrhagic (n = 22) hemispheric stroke and. severe craniocerebral injury with brain contusion (n = 33). Obtained, data testifies to the distinct negative influence of postinsult/ posttraumatic cerebral defect on functional characteristica of counter-lateral ("intact") hemisphere that is reflected in proportional changes of all the spectrum, of analyzed, neurophysiological signs. These changes affects all the tested, modules of neuromotor system, and. can be observed over a long period, after the stroke or craniocerebral injury

Electronic Structure of KFe2_2Se2_2 from First Principles Calculations

Electronic structure and magnetic properties for iron-selenide KFe$_2$Se$_2$ are studied by first-principles calculations. The ground state is stripe-like antiferromagnetic with calculated 2.26 $\mu_B$ magnetic moment on Fe atoms; and the $J_1$, $J_2$ coupling strengths are calculated to be 0.038 eV and 0.029 eV. The states around $E_F$ are dominated by the Fe-3d orbitals which hybridize noticeably to the Se-4p orbitals. While the band structure of KFe$_2$Se$_2$ is similar to a heavily electron-doped BaFe$_2$As$_2$ or FeSe system, the Fermi surface of KFe$_2$Se$_2$ is much closer to \fs11 system since the electron sheets around $M$ is symmetric with respect to $x$-$y$ exchange. These features, as well as the absence of Fermi surface nesting, suggest that the parental KFe$_2$Se$_2$ could be regarded as an electron over-doped 11 system with possible local moment magnetism.Comment: accepted by Chinese Physics Letter, to appear as Chinese Physics Letter, Vol 28, page 057402 (2011

Effects of Ru Substitution on Dimensionality and Electron Correlations in Ba(Fe_{1-x}Ru_x)_2As_2

We report a systematic angle-resolved photoemission spectroscopy study on Ba(Fe$_{1-x}$Ru$_x$)$_2$As$_2$ for a wide range of Ru concentrations (0.15 $\leq$ \emph{x} $\leq$ 0.74). We observed a crossover from two-dimension to three-dimension for some of the hole-like Fermi surfaces with Ru substitution and a large reduction in the mass renormalization close to optimal doping. These results suggest that isovalent Ru substitution has remarkable effects on the low-energy electron excitations, which are important for the evolution of superconductivity and antiferromagnetism in this system.Comment: 4 pages, 4 figure

Band structure of new superconducting AlB_2-like ternary silicides M(Al_{0.5}Si_{0.5})_2 and M(Ga_{0.5}Si_{0.5})_2 (M= Ca, Sr and Ba)

The electronic band structures of the new superconducting (with T_c up to 7.7K) ternary silicides M(A_{0.5}Si_{0.5})_2 (M= Ca, Sr, Ba; A= Al, Ga) in the AlB_2-type structure have been investigated using the full-potential LMTO method. The calculations showed that the trend in transition temperatures doesn't follow the changes in the density d-states at the Fermi level and probably is associated with phonon-mode frequencies.Comment: 7 pagers, 1 table, 7 figure

Electron transport, penetration depth and upper critical magnetic field of ZrB12 and MgB2

We report on the synthesis and measurements of the temperature dependence of resistivity, R(T), the penetration depth, l(T), and upper critical magnetic field, Hc2(T), for polycrystalline samples of dodecaboride ZrB12 and diboride MgB2. We conclude that ZrB12 as well as MgB2 behave like simple metals in the normal state with usual Bloch-Gruneisen temperature dependence of resistivity and with rather low resistive Debye temperature, TR=280 K, for ZrB12 (as compared to MgB2 with TR=900 K). The R(T) and l(T) dependencies of ZrB12 reveal a superconducting transition at Tc=6.0 K. Although a clear exponential l(T)dependence in MgB2 thin films and ceramic pellets was observed at low temperatures, this dependence was almost linear for ZrB12 below Tc/2. These features indicate s-wave pairing state in MgB2, whereas a d-wave pairing state is possible in ZrB12. A fit to the data gives a reduced energy gap 2D(0)/kTc=1.6 for MgB2 films and pellets, in good agreement with published data for 3D \pi - sheets of the Fermi surface. Contrary to conventional theories we found a linear temperature dependence of Hc2(T) for ZrB12 (Hc2(0)=0.15 T).Comment: 8 pages, 10 figures, submitted to JET

Electronic structure and possible pseudogap behavior in iron based superconductors

Starting from the simplified analytic model of electronic spectrum of iron - pnictogen (chalcogen) high - temperature superconductors close to the Fermi level, we discuss the influence of antiferromagneting (AFM)scattering both for stoichiometric case and the region of possible short - range order AFM fluctuations in doped compounds. Qualitative picture of the evolution of electronic spectrum and Fermi surfaces (FS) for different dopings is presented, with the aim of comparison with existing and future ARPES experiments. Both electron and hole dopings are considered and possible pseudogap behavior connected with partial FS "destruction" is demonstrated, explaining some recent experiments.Comment: 5 pages, 4 figures, published versio