1,489 research outputs found
Fermion theories on a 2d torus with Wilson action improved by Pauli -- Villars regularization
Vectorial and anomaly free chiral U(1) fermion models on a 2d finite lattice
are considered. It is demonstrated both numerically and analytically that
introduction of Pauli -- Villars type regularization supresses the symmetry
breaking effects caused by the Wilson term.Comment: 17 pages, Latex, 6 eps-figure
Transport properties and the anisotropy of Ba_{1-x}K_xFe_2As_2 single crystals in normal and superconducting states
The transport and superconducting properties of Ba_{1-x}K_xFe_2As_2 single
crystals with T_c = 31 K were studied. Both in-plane and out-of plane
resistivity was measured by modified Montgomery method. The in-plane
resistivity for all studied samples, obtained in the course of the same
synthesis, is almost the same, unlike to the out-of plane resistivity, which
differ considerably. We have found that the resistivity anisotropy
\gamma=\rho_c /\rho_{ab} is almost temperature independent and lies in the
range 10-30 for different samples. This, probably, indicates on the extrinsic
nature of high out-of-plane resistivity, which may appear due to the presence
of the flat defects along Fe-As layers in the samples. This statement is
supported by comparatively small effective mass anisotropy, obtained from the
upper critical field measurements, and from the observation of the so-called
"Friedel transition", which indicates on the existence of some disorder in the
samples in c-direction.Comment: 5 pages, 5 figure
Ecological ranges and types of rarity in the Kuznetsk Alatau of some Saussurea DC. species
An analysis of indicator values of four Saussurea DC. species, S. baicalensis (Adams) B. L. Rob., S. frolowii Ledeb., S. salicifolia (L.) DC., and S. schanginiana (Wydl.) Fisch. ex Serg., have been carried out by the method of indicator scales of soil moisture and nutrient availability and salinity in more than 1600 relevés. The size of their ecological ranges and the values of their competitiveness in phytocenoses are determined. As a result of a comparison of the locality of local populations within the ecological range and their occurrence, the vulnerability of S. baicalensis, S. frolowii, S. salicifolia, and S. schanginiana in the Kuznetsk Alatau is evaluated. The types of rarity for these species in the Kuznetsk Alatau are determined
Rearrangement of the Fermi Surface of Dense Neutron Matter and Direct Urca Cooling of Neutron Stars
It is proposed that a rearrangement of single-particle degrees of freedom may
occur in a portion of the quantum fluid interior of a neutron star. Such a
rearrangement is associated with the pronounced softening of the spin-isospin
collective mode which, under increasing density, leads to pion condensation.
Arguments and estimates based on fundamental relations of many-body theory show
that one realization of this phenomenon could produce very rapid cooling of the
star via a direct nucelon Urca process displaying a dependence on
temperature.Comment: 8 pages, 2 figure
Normal state resistivity of BaKFeAs: evidence for multiband strong-coupling behavior
We present theoretical analysis of the normal state resistivity in multiband
superconductors in the framework of Eliashberg theory. The results are compared
with measurements of the temperature dependence of normal state resistivity of
high-purity BaKFeAs single crystals with the
highest reported transition temperature = 38.5 K. The experimental data
demonstrate strong deviations from the Bloch-Gr\"{u}neisen behavior, namely the
tendency to saturation of the resistivity at high temperatures. The observed
behavior of the resistivity is explained within the two band scenario when the
first band is strongly coupled and relatively clean, while the second band is
weakly coupled and is characterized by much stronger impurity scattering.Comment: 4 pages, 3 figures, to be published in JETP Letters Vol.94, N
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