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  • IOPscience (Institute of Physics)  (43)
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Year
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  • 1
    Language: English
    In: Russian Mathematical Surveys, 2009, Vol.64(5), pp.787-803
    Description: There are many unsolved problems in discrete mathematics and mathematical cybernetics. Writing a comprehensive survey of such problems involves great difficulties. First, such problems are rather numerous and varied. Second, they greatly differ from each other in degree of completeness of their solution. Therefore, even a comprehensive survey should not attempt to cover the whole variety of such problems; only the most important and significant problems should be reviewed. An impersonal choice of problems to include is quite hard. This paper includes 13 unsolved problems related to combinatorial mathematics and computational complexity theory. The problems selected give an indication of the author's studies for 50 years; for this reason, the choice of the problems reviewed here is, to some extent, subjective. At the same time, these problems are very difficult and quite important for discrete mathematics and mathematical cybernetics. Bibliography: 74 items.
    Keywords: Mathematics;
    ISSN: 0036-0279
    E-ISSN: 1468-4829
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  • 2
    Language: English
    In: Journal of Physics: Condensed Matter, 2011, Vol.23(4), p.045701 (6pp)
    Description: Several experimental and theoretical studies indicate the existence of a critical point separating the underdoped and overdoped regions of the high- T c cuprates phase diagram. There are at least two distinct proposals on the critical concentration and its physical origin. The first one is associated with the pseudogap formation for p 〈 p * , with p * 0.2. The other relies on the Hall effect measurements and suggests that the critical point and the quantum phase transition (QPT) take place at optimal doping, p opt 0.16. Here we have performed a precise density of states calculation and found that there are two QPTs and the corresponding critical concentrations associated with the change of the Fermi surface topology upon doping.
    Keywords: Phases ; Phase Transformations ; Cuprates ; Mathematical Analysis ; Doping ; Mathematical Analysis ; Doping ; Phase Diagrams ; Copper Oxide ; Condensed Matter ; Phase Diagrams ; Phase Transformations ; Optimization ; Critical Point ; Condensed Matter Physics (General) (So) ; General and Nonclassified (Ep) ; General and Nonclassified (Ed) ; General and Nonclassified (EC) ; Physical Metallurgy (CD);
    ISSN: 0953-8984
    E-ISSN: 1361-648X
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  • 3
    Language: English
    In: Physics-Uspekhi, 2014, Vol.57(8), pp.813-819
    Description: Quite recently, the scientific community was shaken up by a new discovery. In the field of high-T sub(c) superconductivity, where cuprates had overwhelmingly predominated for the previous two decades, a new player-iron compounds-has appeared. Although the superconducting transition...
    Keywords: Superconductivity ; Communities ; Single Crystals ; Cuprates ; Copper Oxide ; Transition Temperature ; Transition Temperature ; Electrical Conductivity ; Single Crystals ; Superconductivity ; Solid State Milieux (General) (So) ; Superconductivity (CD) ; Physics (General) (Ah);
    ISSN: 1063-7869
    E-ISSN: 1468-4780
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  • 4
    Language: English
    In: Russian Mathematical Surveys, 2012, Vol.67(1), pp.93-165
    Description: Boolean functions are among the fundamental objects of discrete mathematics, especially in those of its subdisciplines which fall under mathematical logic and mathematical cybernetics. The language of Boolean functions is convenient for describing the operation of many discrete systems such as contact networks, Boolean circuits, branching programs, and some others. An important parameter of discrete systems of this kind is their complexity. This characteristic has been actively investigated starting from Shannon's works. There is a large body of scientific literature presenting many fundamental results. The purpose of this survey is to give an account of the main results over the last sixty years related to the complexity of computation (realization) of Boolean functions by contact networks, Boolean circuits, and Boolean circuits without branching. Bibliography: 165 titles.
    Keywords: Mathematics;
    ISSN: 0036-0279
    E-ISSN: 1468-4829
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  • 5
    Language: English
    In: EPL (Europhysics Letters), 2010, Vol.89(1), p.17004 (5pp)
    Description: We show that the transition of Josephson junctions between the conventional and states caused by the decrease in temperature induces in a regular two-dimensional array of such junctions not just a single phase transition between two phases with different ordering but a sequence of two, three or four phase transitions. The corresponding phase diagrams are constructed for the cases of bipartite (square or honeycomb) and triangular lattices.
    Keywords: Condensed Matter - Superconductivity;
    ISSN: 0295-5075
    E-ISSN: 1286-4854
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  • 6
    Language: English
    In: Journal of Physics: Condensed Matter, 2010, Vol.22(1), p.015701 (6pp)
    Description: Using a LDA+GTB (local density approximation+generalized tight-binding) hybrid scheme we investigate the band structure of the electron-doped high- T c material Sm 2 x Ce x CuO 4 . Parameters of the minimal tight-binding model for this system (the so-called three-band Emery model) were obtained within the NMTO ( N th-order muffin-tin orbital) method. The doping evolution of the dispersion and the Fermi surface in the presence of electronic correlations was investigated in two regimes of magnetic order: short-range (spin-liquid) and long-range (antiferromagnetic metal). Each regime is characterized by the specific topologies of the Fermi surfaces and we discuss their relation to recent experimental data.
    Keywords: Condensed Matter - Strongly Correlated Electrons ; Condensed Matter - Superconductivity;
    ISSN: 0953-8984
    E-ISSN: 1361-648X
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  • 7
    Language: English
    In: Journal of Physics: Conference Series, 2015, Vol.602(1), p.012004 (5pp)
    Description: The article presents the results of analysis of rheology properties of sandy-clay tailings (wastes) of kimberlite ore dressing of the diamond deposit (Russia, Arkhangelsk region). The coefficient of secondary compression as main parameter of soil's creep is defined by implementing standard one-dimensional consolidation test. The linear correlation between initial void ratio and coefficient of secondary compression of sandy-clay tailings were obtained. For numerical simulation of tailing's behaviour subject to its rheology properties in Soft Soil Creep (SSC) model (time independent behaviour) of PLAXIS software was used. According to laboratory tests calibration of SSC model was implemented. It allows predicting dam's safety and reliability for long-term outlook.
    Keywords: Numerische Simulation ; Rheologie ; Labortest ; Eichen (Abgleichen) ; Zeitverhalten ; Russland ; Weicher Boden ; Physics;
    ISSN: 1742-6588
    E-ISSN: 1742-6596
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  • 8
    Language: English
    In: Physica Scripta, 2015, Vol.90(8), p.085203 (5pp)
    Description: The nonlinear dynamics of resistive flow with a chemical reaction is studied. Proceeding from the Lagrangian description, the influence of a chemical reaction on the development of fluid singularities is considered.
    Keywords: Physics - Chemical Physics ; Nonlinear Sciences - Chaotic Dynamics ; Physics - Classical Physics;
    ISSN: 0031-8949
    E-ISSN: 1402-4896
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  • 9
    Language: English
    In: Superconductor Science and Technology, 2018, Vol.31(3), p.034001 (6pp)
    Description: Irradiation of superconductors with different particles is one of many ways to investigate the effects of disorder. Here we study the disorder-induced transition between s ± and s ++ states in the two-band model for Fe-based superconductors with nonmagnetic impurities. Specifically, we investigate the important question of whether the superconducting gaps during the transition change smoothly or abruptly. We show that the behavior can be of either type and is controlled by the ratio of intraband to interband impurity scattering potentials, and by a parameter , that represents scattering strength and ranges from zero (Born approximation) to one (unitary limit). For the pure interband scattering potential and the scattering strength , the transition is accompanied by steep changes in the gaps, while for larger values of , the gaps change smoothly. The behavior of the gaps is characterized by steep changes at low temperatures, with T c0 being the critical temperature in the clean limit, otherwise it changes gradually. The critical temperature T c is always a smooth function of the scattering rate in spite of the steep changes in the behavior of the gaps.
    Keywords: Condensed Matter - Superconductivity;
    ISSN: 0953-2048
    E-ISSN: 1361-6668
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  • 10
    Language: English
    In: IOP Conference Series: Materials Science and Engineering, 2015, Vol.90(1), p.012049 (6pp)
    Description: Methods of designing blades grids of power machines, such as equal thickness shape built on middle-line arc, or methods based on target stress spreading were invented long time ago, well described and still in use. Science and technology has moved far from that time and laboriousness of experimental research, which were involving unique equipment, requires development of new robust and flexible methods of design, which will determine the optimal geometry of flow passage.This investigation provides simple and universal method of designing blades, which, in comparison to the currently used methods, requires significantly less input data but still provides accurate results. The described method is purely analytical for both concave and convex sides of the blade, and therefore lets to describe the curve behavior down the flow path at any point. Compared with the blade grid designs currently used in industry, geometric parameters of the designs constructed with this method show the maximum deviation below 0.4%.
    Keywords: Eingabedaten ; Geometrischer Parameter ; Leistungselement ; Experimentelle Untersuchung ; Engineering;
    ISSN: 1757-8981
    E-ISSN: 1757-899X
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