771 research outputs found
Theoretical investigation of TbNi_{5-x}Cu_x optical properties
In this paper we present theoretical investigation of optical conductivity
for intermetallic TbNi_{5-x}Cu_x series. In the frame of LSDA+U calculations
electronic structure for x=0,1,2 and on top of that optical conductivities were
calculated. Disorder effects of Ni for Cu substitution on a level of LSDA+U
densities of states (DOS) were taken into account via averaging over all
possible Cu ion positions for given doping level x. Gradual suppression and
loosing of structure of optical conductivity at 2 eV together with simultaneous
intensity growth at 4 eV correspond to increase of Cu and decrease of Ni
content. As reported before [Knyazev et al., Optics and Spectroscopy 104, 360
(2008)] plasma frequency has non monotonic doping behaviour with maximum at
x=1. This behaviour is explained as competition between lowering of total
density of states on the Fermi level N(E_F) and growing of number of carriers.
Our theoretical results agree well with variety of recent experiments.Comment: 4 pages, 3 figure
Relativistic description of asymmetric fully heavy tetraquarks in the diquark-antidiquark model
Masses of the ground, orbitally and radially excited states of the asymmetric
fully heavy tetraquarks, composed of charm (c) and bottom (b) quarks and
antiquarks are calculated in the relativistic diquark-antidiquark picture. The
relativistic quark model based on the quasipotential approach and quantum
chromodynamics is used to construct the quasipotentials of the quark-quark and
diquark-antidiquark interactions. These quasipotentials consist of the
short-range one-gluon exchange and long-distance linear confinement
interactions. Relativistic effects are consistently taken into account. A
tetraquark is considered as a bound state of a diquark and an antidiquark which
are treated as a spatially extended colored objects and interact as a whole. It
is shown that most of the investigated tetraquarks states (including all ground
states) lie above the fall-apart strong decay thresholds into a meson pair. As
a result they can be observed as wide resonances. Nevertheless, several
orbitally excited states lie slightly above or even below these fall-apart
thresholds, thus they could be narrow states.Comment: 24 pages, 1 figur
Fight for walls: "patriotic graffiti" as a method of the public imagery formation by pro-Kremlin youth organizations in Russia
Algebraic approach to the spectral problem for the Schroedinger equation with power potentials
The method reducing the solution of the Schroedinger equation for several
types of power potentials to the solution of the eigenvalue problem for the
infinite system of algebraic equations is developed. The finite truncation of
this system provides high accuracy results for low-lying levels. The proposed
approach is appropriate both for analytic calculations and for numerical
computations. This method allows also to determine the spectrum of the
Schroedinger-like relativistic equations. The heavy quarkonium (charmonium and
bottomonium) mass spectra for the Cornell potential and the sum of the Coulomb
and oscillator potentials are calculated. The results are in good agreement
with experimental data.Comment: 17 pages, including 6 PostScript figures (epsf style
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