796 research outputs found
Phase transitions in Bose-Fermi-Hubbard model in the heavy fermion limit: Hard-core boson approach
Phase transitions are investigated in the Bose-Fermi-Hubbard model in the
mean field and hard-core boson approximations for the case of infinitely small
fermion transfer and repulsive on-site boson-fermion interaction. The behavior
of the Bose-Einstein condensate order parameter and grand canonical potential
is analyzed as functions of the chemical potential of bosons at zero
temperature. The possibility of change of order of the phase transition to the
superfluid phase in the regime of fixed values of the chemical potentials of
Bose- and Fermi-particles is established. The relevant phase diagrams are
built.Comment: 20 pages, 15 figure
A Lattice Model of Intercalation
The thermodynamics of the lattice model of intercalation of ions in crystals
is considered in the mean field approximation. Pseudospin formalism is used for
the description of interaction of electrons with ions and the possibility of
hopping of intercalated ions between different positions is taken into account.
Phase diagrams are built. It is shown that the effective interaction between
intercalated ions can lead to phase separation or to appearance of modulated
phase (it depends on filling of the electron energy band). At high values of
the parameter of ion transfer the ionic subsystem can pass to the
superfluid-like state
Geography of European migration
In recent decades, the role of international migration has increased dramatically in most European countries. The growth in migration has made some authors proclaim the beginning of a second Migration Period that could transform the social and cultural identity of Europe. The article presents an analysis of international migration geography in Europe in the last twenty-five years. The authors identify the main trends in migration, provide migration profiles of European countries, and propose a classification based on the recent changes in the migrant stock. Changes in the migrant stock (total emigration and immigration) reflect the level of involvement in international and global processes. They can serve as an indicator of a country's attractiveness for both foreigners and the country’s citizens. The study shows that European countries are increasingly split into "immigrant" and "emigrant" states. The authors describe spatial patterns of migration. The volume and localisation of migration flows in Europe are affected not only by cultural and historical circumstance, such as a colonial past or a common language. The scale of immigrant influx often does not depend on a donor country's demographic potential or the level of its socio-economic development. The links between the place of origin and destination are often more complex than it might initially seem. The authors stress the importance of a differentiated immigration policy taking into account ethnic and cultural features of host societies
Migration flows in Europe: space and time transformation
One of the key manifestations of globalisation is an increase in the spatial mobility of population involving growing numbers of people into international migration processes. This article is an attempt to assess the density of migration connections between European states based on the 1990-2015 quantitative data. An analysis of migration flows and relevant net migration and net migration and migration localisation at the national and regional levels makes it possible to identify key trends in the spatial and temporal transformation of this phenomenon on the European continent. Calculations suggest that an increase in migration has not narrowed the gap between source and recipient countries but, on the contrary, it has made it more pronounced over the recent decades. The article presents an attempt at classifying European countries by the direction and intensity of migration connections and stresses the impact of international migration on the demographic and sociocultural situation in different European states
Interlayer tunneling spectroscopy of BiSrCaCuO: a look from inside on the doping phase diagram of high superconductors
A systematic, doping dependent interlayer tunneling spectroscopy of Bi2212
high superconductor is presented. An improved resolution made it possible
to simultaneously trace the superconducting gap (SG) and the normal state
pseudo-gap (PG) in a close vicinity of and to analyze closing of the PG
at . The obtained doping phase diagram exhibits a critical doping point
for appearance of the PG and a characteristic crossing of the SG and the PG
close to the optimal doping. This points towards coexistence of two different
and competing order parameters in Bi2212. Experimental data indicate that the
SG can form a combined (large) gap with the PG at and that the
interlayer tunneling becomes progressively incoherent with decreasing doping.Comment: 5 pages, 5 figure
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