Experimental evidence of two-band behavior of MgB2

The break-junction tunneling has been systematically investigated in MgB2. Two types of the break-junction contacts have been exploited on the same samples, which demonstrated tunnel contact like (SIS) and point contact like (SnS) behavior. Both of them have shown the existence of the two distinct energy gaps. We have observed also the peculiarities on the I(V)- characteristics related to Leggett's collective mode assisted tunneling. --> Corresponding author address: [email protected]: 14 pages, 6 figures, 1 table; corrected typos and fig

Investigation of LiFeAs by means of "Break-junction" Technique

In our tunneling investigation using Andreev superconductor - normal metal - superconductor contacts on LiFeAs single crystals we observed two reproducible independent subharmonic gap structures at dynamic conductance characteristics. From these results, we can derive the energy of the large superconducting gap $\Delta_L=(2.5 \div 3.4)$ meV and the small gap $\Delta_L=(0.9 \div 1)$ meV at $T = 4.2$ K for the $T_C^{local} \approx (10.5 \div 14)$ K (the contact area critical temperature which deviation causes the variation of $\Delta_L$). The BCS-ratio is found to be $2\Delta_L/k_BT_C = (4.6 \div 5.6)$, whereas $2\Delta_S/k_BT_C \ll 3.52$ results from induced superconductivity in the bands with the small gap.Comment: 7 pages, 5 figures. Published in Pis'ma v ZhETF 95, 604-610 (2012

Influence of epithermal muonic molecule formation on kinetics of the μ\muCF processes in deuterium

The non-resonant formation of $dd\mu$ molecules in the loosely bound state in collisions of non-thermalized $d\mu$ atoms with deuterium molecules D$_2$ has been considered. The process of such a type is possible only for collision energies exceeded the ionization potential of D$_2$. The calculated rates of $dd\mu$ formation in the above-threshold energy region are about one order of magnitude higher than obtained earlier. The role of epithermal non-resonant $\mu$-molecule formation for the kinetics of $\mu$CF processes in D$_2$ gas was studied. It was shown that the non-resonant $dd\mu$ formation by $d\mu$ atoms accelerated during the cascade can be directly observed in the neutron time spectra at very short initial times.Comment: 6 pages, 5 figures, Proceedings of the International Conference on Exotic Atoms and Related Topics EXA-2011, Vienna, Sep 5-9, 201

Observation of Multi-Gap Superconductivity in GdO(F)FeAs by Andreev Spectroscopy

We have studied current-voltage characteristics of Andreev contacts in polycrystalline GdO$_{0.88}$F$_{0.12}$FeAs samples with bulk critical temperature ${T_c}$ = (52.5 \pm 1)K using break-junction technique. The data obtained cannot be described within the single-gap approach and suggests the existence of a multi-gap superconductivity in this compound. The large and small superconducting gap values estimated at T = 4.2K are {\Delta}L = 10.5 \pm 2 meV and {\Delta}S = 2.3 \pm 0.4 meV, respectively.Comment: 5 pages, 4 figures, submitted to JETP Letter

Doping effect on the anomalous behavior of the Hall effect in electron-doped superconductor Nd2−x_{2-x}Cex_xCuO4+δ_{4+\delta}

Transport properties of Nd$_{2-x}$Ce$_x$CuO$_{4+\delta}$ single crystal films are investigated in magnetic fields $B$ up to 9T at $T$=(0.4-4.2)K. An analysis of normal state (at $B>B_{c2}$) Hall coefficient $R_H$$^n$ dependence on Ce doping takes us to a conclusion about the existence both of electron-like and hole-like contributions to transport in nominally electron-doped system. In accordance with $R_H$$^n$(x) analysis an anomalous sign reversal of Hall effect in mixed state at $B<B_{c2}$ may be ascribed to a flux-flow regime for two types of carriers with opposite charges.Comment: 14 pages, 5 figure

Sudden drop of fractal dimension of electromagnetic emissions recorded prior to significant earthquake

The variation of fractal dimension and entropy during a damage evolution process, especially approaching critical failure, has been recently investigated. A sudden drop of fractal dimension has been proposed as a quantitative indicator of damage localization or a likely precursor of an impending catastrophic failure. In this contribution, electromagnetic emissions recorded prior to significant earthquake are analysed to investigate whether they also present such sudden fractal dimension and entropy drops as the main catastrophic event is approaching. The pre-earthquake electromagnetic time series analysis results reveal a good agreement to the theoretically expected ones indicating that the critical fracture is approaching

Roles of GM-CSF in the Pathogenesis of Autoimmune Diseases: An Update.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) was first described as a growth factor that induces the differentiation and proliferation of myeloid progenitors in the bone marrow. GM-CSF also has an important cytokine effect in chronic inflammatory diseases by stimulating the activation and migration of myeloid cells to inflammation sites, promoting survival of target cells and stimulating the renewal of effector granulocytes and macrophages. Because of these pro-cellular effects, an imbalance in GM-CSF production/signaling may lead to harmful inflammatory conditions. In this context, GM-CSF has a pathogenic role in autoimmune diseases that are dependent on cellular immune responses such as multiple sclerosis (MS) and rheumatoid arthritis (RA). Conversely, a protective role has also been described in other autoimmune diseases where humoral responses are detrimental such as myasthenia gravis (MG), Hashimoto\u27s thyroiditis (HT), inflammatory bowel disease (IBD), and systemic lupus erythematosus (SLE). In this review, we aimed for a comprehensive analysis of literature data on the multiple roles of GM-CSF in autoimmue diseases and possible therapeutic strategies that target GM-CSF production

Identification of the bulk pairing symmetry in high-temperature superconductors: Evidence for an extended s-wave with eight line nodes

we identify the intrinsic bulk pairing symmetry for both electron and hole-doped cuprates from the existing bulk- and nearly bulk-sensitive experimental results such as magnetic penetration depth, Raman scattering, single-particle tunneling, Andreev reflection, nonlinear Meissner effect, neutron scattering, thermal conductivity, specific heat, and angle-resolved photoemission spectroscopy. These experiments consistently show that the dominant bulk pairing symmetry in hole-doped cuprates is of extended s-wave with eight line nodes, and of anisotropic s-wave in electron-doped cuprates. The proposed pairing symmetries do not contradict some surface- and phase-sensitive experiments which show a predominant d-wave pairing symmetry at the degraded surfaces. We also quantitatively explain the phase-sensitive experiments along the c-axis for both Bi_{2}Sr_{2}CaCu_{2}O_{8+y} and YBa_{2}Cu_{3}O_{7-y}.Comment: 11 pages, 9 figure

Central nervous system (CNS)–resident natural killer cells suppress Th17 responses and CNS autoimmune pathology

Natural killer (NK) cells of the innate immune system can profoundly impact the development of adaptive immune responses. Inflammatory and autoimmune responses in anatomical locations such as the central nervous system (CNS) differ substantially from those found in peripheral organs. We show in a mouse model of multiple sclerosis that NK cell enrichment results in disease amelioration, whereas selective blockade of NK cell homing to the CNS results in disease exacerbation. Importantly, the effects of NK cells on CNS pathology were dependent on the activity of CNS-resident, but not peripheral, NK cells. This activity of CNS-resident NK cells involved interactions with microglia and suppression of myelin-reactive Th17 cells. Our studies suggest an organ-specific activity of NK cells on the magnitude of CNS inflammation, providing potential new targets for therapeutic intervention

Erythropoietin: A potent inducer of peripheral immuno/inflammatory modulation in autoimmune EAE

Background: Beneficial effects of short-term erythropoietin (EPO) theraphy have been demonstrated in several animal models of acute neurologic injury, including experimental autoimmune encephalomyelitis(EAE)-the animal model of multiple sclerosis. We have found that EPO treatment substantially reduces the acute clinical paralysis seen EAE mice and this improvements is accompanied by a large reduction in the mononuclear cell infiltration and downregulation of glial MHC class II expression within the inflamed CNS. Other reports have recently indicated that peripherally generated anti-inflammatory CD4 +Foxp3 3 regulatory T cells (Tregs) and the IL17-producing CD4+ T helper cell (Th17) subpopulations play key antagonistic roles in EAE pathogenesis. However, no information regardind the effects of EPO theraphy on the behavior of the general mononuclear-lymphocyte population, Tregs or Th17 cells in EAE has emerged. Methods and Findings: We first determined in vivo that EPO theraphy markedly suppressed MOG specific T cell proliferation and sharply reduced the number of reactive dendritic cells (CD11c positive) in EAE lumph modes during both inductive and later symptomatic phases of MOG 35-55 induced EAE. We then determined the effect in vivo of EPO on numbers of peripheral Treg cells and Th17 cells. We found that EPO treatment modulated immune balance in both the periphery and the inflamed spinal cord by promoting a large expansion in Treg cells, inhibiting Th17 polarization and abrogating proliferation of the antigen presenting dendritic cell population. Finally we utilized tissue culture assays to show that exposure to EPO in vitro similarly downregulated MOG-specific T cell proliferation and also greatly suppressed T cell production of pro-inflammatory cytokines. Conclusions: Taken together, our findings reveal an important new locus whereby EPO induces substantial long-term tissue protection in the host through signalling to several critical subsets of immune cells that reside in the peripheral lymphatic system.published_or_final_versio