2,683 research outputs found
Calculation of intensity of high energy muon groups observed deep underground
The intensity of narrow muon groups observed in Kolar Gold Field (KGF) at the depth of 3375 m.w.e. was calculated in terms of quark-gluon strings model for high energy hadron - air nuclei interactions by the method of direct modeling of nuclear cascade in the air and muon propagation in the ground for normal primary cosmic ray composition. The calculated intensity has been found to be approx. 10 to the 4 times less than one observed experimentally
Interplay of paramagnetic, orbital and impurity effects on the phase transition of a normal metal to superconducting state
We derive the generalized Ginzburg-Landau free energy functional for
conventional and unconventional singlet superconductors in the presence of
paramagnetic, orbital and impurity effects. Within the mean field theory, we
determine the criterion for appearence of the non uniform
(Fulde-Ferrell-Larkin-Ovchinnikov) superconducting state, with vortex lattice
structure and additional modulation along the magnetic field. We also discuss
the possible change of the order of transition from normal to superconducting
state. We find that the superconducting phase diagram is very sensitive to
geometrical effects such as the nature of the order parameter and the shape of
the Fermi surface. In particular, we obtain the qualitative phase diagrams for
three-dimensional isotropic s-wave superconductors and in quasi two-dimensional
d-wave superconductors under magnetic field perpendicular to the conducting
layers.
In addition, we determine the criterion for instability toward non uniform
superconducting state in s-wave superconductors in the dirty limit.Comment: 15 pages, 4 figure
Immunogenetic profile of MIC (A, B) HLA loci linked to MHC antigenic complex in Russians of the Chelyabinsk Region
The MIC genes are located on chromosome 6 in the class I major histocompatibility complex (MHC) region and encode a membrane-bound stress-inducible protein that acts as a ligand to stimulate the NKG2D activating receptor expressed on the surface of the most natural killer cells (NK). Currently, 7 MIC loci are known, of which only MICA and MICB encode proteins and show a significant allelic polymorphism. The MIC gene polymorphism and their location in the HLA region suggests presence of some ethnic and populational differences for the gene frequencies, linkage disequilibrium of distinct loci, and distribution of HLA-MIC haplotypes, thus making it possible to get information on genetic relationship of human populations. The aim of our study was to assess immunogenetic profile of Russian population in Chelyabinsk Region based on the non-classical HLA loci, i.e., MICA and MICB, in the context of worldwide population data. Methods of the study included immunogenetic typing of 100 donors identifying themselves as Russians, taken from the Registry of Stem Cell Donors at the Chelyabinsk Regional Blood Transfusion Station. The 2 loci (MICA and MICB) were typed at basic resolution, using PCR technique with sequence-specific primers (SSP-PCR). Gene frequencies (GF) were calculated using programs for immunogenetic research (Arlequin 3.5).Among Russian population from Chelyabinsk Region, the following characteristics of the MICA gene distributions were found: MICA *008, *002, *010, *009, frequency of > 7%; average frequencies, for MICA *004, *007, *018, *017; whereas MICA *027, *011, *006, *009:02, *049, *012, *016 was registered at a frequency of < 3.5%. MICB gene profile was as follows: MICB *005:02, *004, *002, *008 at a frequency of > 6%; at a frequency of 4% MICB *003, *005:03; MICB *005:01, * 005:04, * 009N, MICB *013, *014 at a frequency of0.5%. As based on calculated genetic distances (according to Ney) for the MICA locus, the dendrogram and scatter plot were designed by means of multidimensional scaling (MDS) method, presenting location of 30 world populations, including data on Russians in Chelyabinsk Region. The smallest genetic distances between the population of Russians from Chelyabinsk Region and other world populations were found between the population of Slovenia, as well as the USA population of European origin. As based on scatterplot obtained by the MDS approach for MICA gene frequencies, using the data of cluster analysis, we have found that the population of Russians from Chelyabinsk Region belongs to a cluster of typical European populations.The obtained patterns could be used for practical purposes to create a registry of stem cell donors in Russia. In addition, the data may be used as a control group for further research in the area of HLA-disease association, and could be also demanded by the specialists in population ethnogenesis
Andreev levels in a single-channel conductor
We calculate the subgap density of states of a disordered single-channel
normal metal connected to a superconductor at one end (NS junction) or at both
ends (SNS junction). The probability distribution of the energy of a bound
state (Andreev level) is broadened by disorder. In the SNS case the two-fold
degeneracy of the Andreev levels is removed by disorder leading to a splitting
in addition to the broadening. The distribution of the splitting is given
precisely by Wigner's surmise from random-matrix theory. For strong disorder
the mean density of states is largely unaffected by the proximity to the
superconductor, because of localization, except in a narrow energy region near
the Fermi level, where the density of states is suppressed with a log-normal
tail.Comment: 12 pages, 5 figure
Stochastic pump effect and geometric phases in dissipative and stochastic systems
The success of Berry phases in quantum mechanics stimulated the study of
similar phenomena in other areas of physics, including the theory of living
cell locomotion and motion of patterns in nonlinear media. More recently,
geometric phases have been applied to systems operating in a strongly
stochastic environment, such as molecular motors. We discuss such geometric
effects in purely classical dissipative stochastic systems and their role in
the theory of the stochastic pump effect (SPE).Comment: Review. 35 pages. J. Phys. A: Math, Theor. (in press
Anisotropic Impurity-States, Quasiparticle Scattering and Nematic Transport in Underdoped Ca(Fe1-xCox)2As2
Iron-based high temperature superconductivity develops when the `parent'
antiferromagnetic/orthorhombic phase is suppressed, typically by introduction
of dopant atoms. But their impact on atomic-scale electronic structure, while
in theory quite complex, is unknown experimentally. What is known is that a
strong transport anisotropy with its resistivity maximum along the crystal
b-axis, develops with increasing concentration of dopant atoms; this
`nematicity' vanishes when the `parent' phase disappears near the maximum
superconducting Tc. The interplay between the electronic structure surrounding
each dopant atom, quasiparticle scattering therefrom, and the transport
nematicity has therefore become a pivotal focus of research into these
materials. Here, by directly visualizing the atomic-scale electronic structure,
we show that substituting Co for Fe atoms in underdoped Ca(Fe1-xCox)2As2
generates a dense population of identical anisotropic impurity states. Each is
~8 Fe-Fe unit cells in length, and all are distributed randomly but aligned
with the antiferromagnetic a-axis. By imaging their surrounding interference
patterns, we further demonstrate that these impurity states scatter
quasiparticles in a highly anisotropic manner, with the maximum scattering rate
concentrated along the b-axis. These data provide direct support for the recent
proposals that it is primarily anisotropic scattering by dopant-induced
impurity states that generates the transport nematicity; they also yield simple
explanations for the enhancement of the nematicity proportional to the dopant
density and for the occurrence of the highest resistivity along the b-axis
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