69,480 research outputs found
Network structure of phonographic market with characteristic similarities between musicians
We investigate relations between best selling artists in last decade on
phonographic market and from perspective of listeners by using the Social
Network Analyzes. Starting network is obtained from the matrix of correlations
between the world's best selling artists by considering the synchronous time
evolution of weekly record sales. This method reveals the structure of
phonographic market, but we claim that it has no impact on people who see
relationship between artists and music genres. We compare 'sale' (based on
correlation of record sales) or 'popularity' (based on data mining of the
record charts) networks with 'similarity' (obtained mainly from survey within
music experts opinion) and find no significant relations. We postulate that
non-laminar phenomena on this specific market introduce turbulence to how
people view relations of artists.Comment: 15
Monochromatic loose paths in multicolored -uniform cliques
For integers and , a -uniform hypergraph is called a
loose path of length , and denoted by , if it consists of
edges such that if and
if . In other words, each pair of
consecutive edges intersects on a single vertex, while all other pairs are
disjoint. Let be the minimum integer such that every
-edge-coloring of the complete -uniform hypergraph yields a
monochromatic copy of . In this paper we are mostly interested in
constructive upper bounds on , meaning that on the cost of
possibly enlarging the order of the complete hypergraph, we would like to
efficiently find a monochromatic copy of in every coloring. In
particular, we show that there is a constant such that for all ,
, , and , there is an
algorithm such that for every -edge-coloring of the edges of , it
finds a monochromatic copy of in time at most . We also
prove a non-constructive upper bound
Bulk motion Comptonization in black-hole accretion flows
We study spectra generated by Comptonization of soft photons by cold
electrons radially free-falling onto a black hole. We use a Monte Carlo method
involving a fully relativistic description of Comptonization in the Kerr
space-time. In agreement with previous studies, we find that Comptonization on
the bulk motion of free fall gives rise to power-law spectra with the photon
index of Gamma >~ 3. In contrast to some previous studies, we find that these
power-law spectra extend only to energies << 511 keV. We indicate several
effects resulting in generic cutoffs of such spectra at several tens of keV,
regardless of any specific values of physical parameters in the model. This
inefficiency of producing photons with energies > 100 keV rules out bulk motion
Comptonization as a main radiative process in soft spectral states of
black-hole binaries. The normalization of the power law (below the cutoff) with
respect to the peak of the blackbody emission of the surrounding disc is
typically very low, except for models with an overlap between the disc and the
plasma, in which case the spectra are very soft, Gamma >~ 4.Comment: 10 pages, 4 figures, revised version, accepted for publication in
MNRA
Metallization of solid molecular hydrogen in two dimensions: Mott-Hubbard-type transition
We analyze the pressure-induced metal-insulator transition in a
two-dimensional vertical stack of molecules in x-y plane, and show that
it represents a striking example of the Mott-Hubbard-type transition. Our
combined exact diagonalization approach, formulated and solved in the second
quantization formalism, includes also simultaneous ab initio readjustment of
the single-particle wave functions, contained in the model microscopic
parameters. The system is studied as a function of applied side force
(generalized pressure), both in the -molecular and -quasiatomic states.
Extended Hubbard model is taken at the start, together with longer-range
electron-electron interactions incorporated into the scheme. The stacked
molecular plane transforms discontinuously into a (quasi)atomic state under the
applied force via a two-step transition: the first between molecular insulating
phases and the second from the molecular to the quasiatomic metallic phase. No
quasiatomic insulating phase occurs. All the transitions are accompanied by an
abrupt changes of the bond length and the intermolecular distance (lattice
parameter), as well as by discontinuous changes of the principal electronic
properties, which are characteristic of the Mott-Hubbard transition here
associated with the jumps of the predetermined equilibrium lattice parameter
and the effective bond length. The phase transition can be interpreted in terms
of the solid hydrogen metallization under pressure exerted by e.g., the
substrate covered with a monomolecular film of the vertically stacked
molecules. Both the Mott and Hubbard criteria at the insulator to metal
transition are discussed
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