28 research outputs found
Consistent low-energy reduction of the three-band model for copper oxides with O-O hopping to the effective t-J model
A full three-band model for the CuO plane with inclusion of all
essential interactions - Cu-O and O-O hopping, repulsion at the copper and
oxygen and between them - is considered. A general procedure of the low-energy
reduction of the primary Hamiltonian to the Hamiltonian of the generalized
-- model is developed. An important role of the direct O-O hopping is
discussed. Parameters of the effective low-energy model (the hopping integral,
the band position and the superexchange constant are calculated. An
analysis of the obtained data shows that the experimental value of fixes
the charge transfer energy in a narrow
region of energies.Comment: 32 pp. (LATEX), two figures (PostScript) appende
Range of the t--J model parameters for CuO plane: experimental data constraints
The t-J model effective hopping integral is determined from the three-band
Hubbard model for the charge carriers in CuO plane. For this purpose the
values of the superexchange constant and the charge-transfer gap
are calculated in the framework of the three-band model. Fitting values of
and to the experimental data allows to narrow the uncertainty region
of the three-band model parameters. As a result, the ratio of the t-J
model is fixed in the range for holes and for
electrons. Formation of the Frenkel exciton is justified and the main features
of the charge-transfer spectrum are correctly described in the framework of
this approach.Comment: 20pp., REVTEX 3.0, (11 figures), report 66
High Power Electric Propulsion: MARS plus EUROPA – Already Beyond 2025!
It’s mid-term realization plus global strategic investments: the results of the European Russian DEMOCRITOS project (Horizon 2020) related to the MW class INPPS (International Nuclear Power and Propulsion System) flagship will be described. INPPS flagship includes high power electric thrusters cluster, supplied electric power by the nuclear reactor (successfully tested in Russia) and a solar power ring. Two INPPS versions were studied – the wide and arrow wing versions. Both versions have a futuristic design with standardized interfaces for several flagship subsystems. Especially the high payload mass of INPPS allows the transport of – for example – up to 12 t to JUPITER moon EUROPA and about 18 t to MARS – as a function of specific impulse of electric thrusters.
INPPS flagship not only allows scientific, but especially commercial and communication payloads as well. This means industrial-scale production of space flight systems for robotic and human space exploration.
International cooperation related to INPPS realization are necessary within an International High Power Space Transportation program to realize the DEMOCRITOS core, ground and space components until 2025.
DEMOCRITOS project included partners from Europe, Russia and a Brazilian guest observer and received several inputs from NASA Cleveland and JAXA Tokyo
Lifshitz quantum phase transitions and Fermi surface transformation with hole doping in high- superconductors
We study the doping evolution of the electronic structure in the normal phase
of high- cuprates. Electronic structure and Fermi surface of cuprates with
single CuO layer in the unit cell like LaSrCuO have been
calculated by the LDA+GTB method in the regime of strong electron correlations
(SEC) and compared to ARPES and quantum oscillations data. We have found two
critical concentrations, and , where the Fermi surface
topology changes. Following I.M. Lifshitz ideas of the quantum phase
transitions (QPT) of the 2.5-order we discuss the concentration dependence of
the low temperature thermodynamics. The behavior of the electronic specific
heat is similar to the Loram and Cooper
experimental data in the vicinity of .Comment: 8 pages, 4 figure
Geography of “Archival continents” of Russian Diaspora: history of formation
The article analyzes the process of the establishment of archival continents of the Russian diaspora and the causes of the emergence of foreign archival Rossica. The article reveals the influence of migrations on this process. Authors show the diversity of archival materials on the Russian history which are kept outside Russia and often scattered in different archival collections, private and public archives and libraries. The emergence of communities of the Russian diaspora in several countries of the world led to the formation of extensive archival heritage. The study of this heritage is one the most urgent contemporary problems. The activities related to the discovery, restitution to Russia and use of this heritage have significantly increased in the last decades which is connected with the change of the political situation, researchers’ gaining access to the archival collections of the Russian diaspora. The relevance of this fundamental research problem is enhanced by the necessity of eliminating the existing information gap at the current stage of the Russian history development - to reveal the information concerning foreign archival Rossica, the documents of the Russian diaspora and their locations in foreign archives and compile them in the unified information data base. The identification of the location of different documents of this group is aimed at the reconstruction of the integrity of the scattered archival collections by means of both restitution, exchange or copying of the documents and by means of virtual unification, for example, in the form of digital archive. These activities will also contribute to solving the problems related to the restitution of the archival heritage
Investigation of discharge channel wall material influence on lifetime of hall effect thruster with high specific impulse
Results of 500-hour life tests of the 900-watt Hall-thruster laboratory model with the specific impulse of 2000 s are presented. The thruster discharge channel walls were manufactured from 60% BN + 40% SiO2 and >90% BN hot-pressed ceramics. The predicted total lifetime was ∼3000 h for both wall materials in spite of greater erosion resistance of pure BN in comparison with BN-SiO2 mixture. To clarify the accompanying phenomena, the following diagnostics were carried out. The surface microstructure and composition insulators were investigated by means of electron microscopy and X-ray fluorescence analysis and nearwall plasma parameters were measured with flat Langmuir probes. The obtained distributions of plasma parameters were compared with the results of stationary one-dimensional (1D) hydrodynamic modeling of discharge channel