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1.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Sidorov K. A., Tikhonov N. V., Ovchinnikov S. G.
Заглавие : Exact solution for the thermodynamics of the one-dimensional Hubbard model with infinite repulsion in a magnetic field
Коллективы : Russian Federation Ministry of Education and Science [SFU 2014 GF-2]; Presidium of the Russian Academy of Sciences [20.7]; Program for Supporting Leading Scientific Schools [NSh-1044.2012.2]; Russian Foundation [10-02-00251]; Siberian Federal University [NF-11]
Место публикации : Theor. Math. Phys.: MAIK Nauka-Interperiodica / Springer, 2014. - Vol. 180, Is. 1. - P.835-849. - ISSN 0040-5779, DOI 10.1007/s11232-014-0183-9. - ISSN 1573-9333
Примечания : Cited References: 8. - This work was supported in part by the Russian Federation Ministry of Education and Science (State Order SFU 2014 GF-2), the Presidium of the Russian Academy of Sciences (Program No. 20.7), the Program for Supporting Leading Scientific Schools (Grant No. NSh-1044.2012.2), the Russian Foundation for Basic Research (Grant No. 10-02-00251), and the Siberian Federal University (Internal Grant No. NF-11).
Предметные рубрики: FINITE TEMPERATURES
Ключевые слова (''Своб.индексиров.''): hubbard model--magnetic field--infinite repulsion--thermodynamics--exact solution
Аннотация: We demonstrate that in the limit of infinite repulsion in a magnetic field, the canonical partition function of the one-dimensional Hubbard model in the nearest-neighbor approximation factors into the product of partition functions of holons and spinons, which can be calculated exactly. We thus obtain exact numerical dependences of the free energy, entropy, internal energy, specific heat, chemical potential, and magnetic susceptibility on the hole concentration, temperature, and magnetic field induction.
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2.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Gorev M. V., Aleksandrov K. S.
Заглавие : Effect of hydrostatic pressure on phase transitions in perovskite-like ferroelastics
Коллективы : Russian-Japanese symposium on ferroelectricity
Место публикации : Ferroelectrics: Proceedings of the 1994 5th Russian-Japanese Symposium on Ferroelectricity. Part 2 (of 2). - 1995. - Vol. 169, Is. 1. - P.199-205. - ISSN 0015-0193, DOI 10.1080/00150199508217330
Ключевые слова (''Своб.индексиров.''): crystals--hydrostatic pressure--mathematical models--perovskite--phase transitions--pressure effects--thermodynamics--perovskite like ferroelastics--ferroelectric materials
Аннотация: The analysis of hydrostatic pressure influence on ferroelastic phase transitions in three- and two-dimensional perovskite-like crystals is carried out. The nonlinear effects and the change of the dT0/dp sign are discussed on the ground of the thermodynamic theory. Simple model of rigid spheres is used to connect the T0 shift under pressure with the bonds stresses.
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3.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Flerov I. N., Aleksandrov K. S., Tressaud A., Grannec J., Couzi M.
Заглавие : Phase transitions in elpasolites (ordered perovskites)
Место публикации : Materials Science and Engineering R: Reports. - 1998. - Vol. 24, Is. 3. - P.81-151. - ISSN 0927-796X
Примечания : Cited References: 174
Предметные рубрики: ELASTIC NEUTRON-DIFFRACTION
MII = CO
RAMAN-SCATTERING
THERMODYNAMIC PROPERTIES
CRYSTAL-STRUCTURE
SINGLE-CRYSTALS
RB2KMIIIF6 ELPASOLITES
CUBIC PEROVSKITES
TEMPERATURE FORM
HIGH-RESOLUTION
Ключевые слова (''Своб.индексиров.''): crystal atomic structure--crystal growth--crystal lattices--crystallization--crystallography--ferroelectricity--hydrostatic pressure--order disorder transitions--single crystals--thermodynamics--elpasolites--landau theory--perovskite
Аннотация: Many compounds with general chemical formula A2BB?X6 and with tolerance factor value t < 1 crystallize in the elpasolite (ordered perovskite) structure. Different preparative methods have been considered. For example, the Bridgman technique is the most suitable method of growing single crystals of halogenated elpasolites with monoatomic cations. Group-theory and symmetry analyses have allowed us to build a scheme of possible structural distortions connected with octahedral rotations and displacements of ions. Experimental observations have proven that ferroelastic phase transitions occurring most frequently in elpasolites are due to small octahedra tilts. Quantitative analysis allows the possibility of describing these transitions in the framework of the thermodynamic Landau theory. Hydrostatic pressure and the substitution of atoms in different crystallographic sites allow to change significantly the succession and the temperature of phase transitions. The hypothesis of bond stresses is able to predict the possible occurrence of a phase transition for a particular elpasolite and/or the role of the octahedra rotations in the transformation. The mechanism of phase transitions in elpasolites and related compounds has also been considered. One can assume that a displacive mechanism associated with a strong anharmonicity plays a large role in phase transitions occurring in compounds with monoatomic cations. On the other hand, for instance, in cryolites with ammonium cations, the transitions originate from an order-disorder phenomenon. В© 1998 Elsevier Science S.A. All rights reserved.
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4.

Вид документа : Статья из сборника (выпуск продолж. издания)
Шифр издания :
Автор(ы) : Mironov V. L., Molostov I. P., Scherbinin V. V.
Заглавие : Dielectric model of a mineral arctic soil thawed and frozen at 0.05-15 GHz
Коллективы : International Siberian Conference on Control and Communications
Место публикации : Int. Sib. Conf. on Control and Communicat. (SIBCON 2015): Proceedings: IEEE-Institute Electrical and Electronics Engineers, 2015. - P.1-7. - , DOI 10.1109/SIBCON.2015.7147146
Ключевые слова (''Своб.индексиров.''): arctic regions--dielectric model--dielectric relaxation--remote sensing--soil--temperature dependence--dielectric relaxation--moisture--remote sensing--soil moisture--soils--temperature--temperature distribution--thawing--thermodynamics--active and passive remote sensing--arctic regions--complex dielectric constant--dielectric modeling--soil dielectric constant--spectroscopic parameters--temperature dependence--thermodynamics parameters--soil surveys
Аннотация: The dielectric model for an arctic soil both thawed and frozen has been developed. The model is based on the soil dielectric measurements carried out in the ranges of gravimetric moisture from 0.01 to 0.43 g/g, dry soil density from 1.25 to 1.83 g/cm3, and temperature from 25 to -30°C (cooling run), in the frequency range 0.05-15 GHz. To fit the results of measurements of the soil complex dielectric constant as a function of soil moisture and wave frequency, the refractive mixing dielectric model in conjunction with the Debye multi-relaxation equations were applied. As a result, the spectroscopic parameters of dielectric relaxations for the bound, transient bound, and unbound soil water components were derived, being further complimented with the thermodynamics parameters to ensure a complete set of parameters of the temperature dependent multi-relaxation spectroscopic dielectric model for moist soils proposed. To calculate complex dielectric constant of soil, the following input variables have to be assigned: 1) density of dry soil, 2) gravimetric moisture, 3) wave frequency, and 4) temperature. The error of the dielectric model was evaluated in terms of RMSE, yielding the values RMSE of 0.53 and 0.43 for the soil dielectric constant and loss factor, respectively. These values appeared to be in the order of the dielectric measurement error itself. The dielectric model suggested can be applied in the active and passive remote sensing techniques in microwave to develop algorithms for retrieving soil moisture and freeze/thaw state of the topsoil in the Arctic regions. © 2015 IEEE.
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5.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Ovchinnikov S. G., Sidorov K. A., Shneyder E. I.
Заглавие : Anomalous thermodynamics of the doped Mott-Hubbard insulators
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2011. - Vol. 53, Is. 2. - P299-302. - ISSN 1063-7834, DOI 10.1134/S1063783411020247
Примечания : Cited References: 6. - This study was supported by the Russian Foundation for Basic Research (project no. 09-02-00127), the Branch of the Physical Sciences of the Russian Academy of Sciences (program nos. 2 and 3), grant no. MK-1683.2010.2, and by the Federal Target Program "Personnel" (project NK-589 P).
Предметные рубрики: T-J MODEL
SPECTRUM
Аннотация: The concentration dependence of the entropy of doped Mott-Hubbard insulators has been considered within the t-J model. It has been shown that a change in the type and statistics of charge carriers as compared to the Fermi gas leads to a radical change in the entropy s, in particular, to the giant growth of the entropy upon doping. The quantity a,s/a,x a parts per thousand k (B) is approximately consistent with the experimental data for HTSC cuprates in the pseudogap phase.
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6.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov A. S., Sorokin P. B., Kuzubov A. A.
Заглавие : Ab initio study of hydrogen chemical adsorption on platinum surface/carbon nanotube join system
Место публикации : Phys. Status Solidi B. - 2008. - Vol. 245, Is. 8. - P.1546-1551. - ISSN 0370-1972, DOI 10.1002/pssb.200844155
Примечания : Cited References: 31
Предметные рубрики: WALLED CARBON NANOTUBES
MOLECULAR-DYNAMICS
ROOM-TEMPERATURE
STORAGE
ENERGY
THERMODYNAMICS
GRAPHITE
DENSITY
POINTS
Аннотация: The process of hydrogen chemical adsorption on platinum cluster/single wall carbon nanotube (CNT) join surfaces is modelled at various temperatures and pressures. For that, the adsorption energy of hydrogen atoms on surfaces of both platinum (111) plate and CNT (5,5) or (8,8) types is calculated by density functional theory with the PBE approximation. At various temperatures the hydrogen atom hopping rate on both platinum and CNT surfaces is calculated by the transition state theory. Furthermore the hydrogen hopping rate from the platinum surface to the attached nanotube is obtained by calculation of the total energy profile. It is proved that hydrogen atoms can migrate easily at the platinum surface at all temperatures, but at the CNT surface they can migrate beginning at 400-500 K. By calculation of chemical potentials of hydrogen in gas or on CNT or platinum cluster surfaces the equilibrium density of adsorbed hydrogen was calculated at different temperatures and pressures. It is established that for all temperatures in the range 300-900 K and for all pressures less than 500 bar, the hydrogen is dissociated and chemically adsorbed on the platinum surface very effectively, but surface site occupation by hydrogen on attached CNT surface is rather small. But if CNT vacancies are present in the tube structure and the temperature is lower then 450 K, hydrogen atoms can be adsorbed effectively enough on these vacancies. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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7.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Popova E. A., Tristan N., Vasiliev A. N., Temerov V. L., Bezmaternykh L. N., Leps N., Buechner B., Klingeler R.
Заглавие : Magnetization and specific heat of DyFe3(BO3)(4) single crystal
Разночтения заглавия :авие SCOPUS: Magnetization and specific heat of DyFe 3(BO 3) 4 single crystal
Место публикации : Eur. Phys. J. B: SPRINGER, 2008. - Vol. 62, Is. 2. - P123-128. - ISSN 1434-6028, DOI 10.1140/epjb/e2008-00146-5
Примечания : Cited References: 18
Предметные рубрики: IRON
NDFE3(BO3)(4)
GDFE3(BO3)(4)
Ключевые слова (''Своб.индексиров.''): antiferromagnetic orders--iron subsystems--antiferromagnetic materials--dysprosium compounds--magnetic field effects--magnetization--specific heat--thermodynamics--single crystals
Аннотация: We present thermodynamic and magnetic studies of single crystalline DyFe3(BO3)(4). The data indicate an easy axis antiferromagnetic order below T-N similar to 38 K which we attribute to the Fe subsystem. The Dy subsystem remains paramagnetic down to the lowest investigated temperatures of 2 K, but it is polarized by the Fe spins due to a f-d interaction. External magnetic field leads to a spin-flop transition in the iron subsystem as well as to superposed magnetization in the Dy subsystem. The repopulation of two low-lying Kramers doublets in Dy3+ ions results in well defined Schottky anomalies in specific heat and magnetization.
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8.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Gekht R. S., Bondarenko I. N.
Заглавие : A quantum spin liquid in a two-layer triangular antiferromagnet
Место публикации : J. Exp. Theor. Phys.: AMER INST PHYSICS, 2005. - Vol. 101, Is. 5. - P868-880. - ISSN 1063-7761, DOI 10.1134/1.2149066
Примечания : Cited References: 43
Предметные рубрики: ONE-DIMENSIONAL ANTIFERROMAGNETS
DIMER GROUND-STATE
MEAN-FIELD THEORY
HEISENBERG-ANTIFERROMAGNET
SYSTEM SRCU2(BO3)(2)
PHASE-TRANSITION
GAP
FLUCTUATIONS
EXCITATIONS
LATTICE
Ключевые слова (''Своб.индексиров.''): antiferromagnetic materials--magnetic fields--magnetization--phase diagrams--spectrum analysis--thermodynamics--analogous systems--square lattices--thermodynamic quantities--two-layer triangular antiferromagnets--quantum theory
Аннотация: The possibility of implementing a quantum-spin-liquid-type state in a two-layer triangular spin-1/2 antiferromagnet at T = 0 is investigated. The ratio of intra- to interlayer exchange constants (j) is found under which a transition from the classical state with 120 degrees triangular order to a quantum state with zero magnetization per site occurs; in this case, the spins of adjacent layers form singlets that are separated from triplet excitations by an energy gap. Compared with an analogous system with the square lattice, the range of j in which the classical ordered state is realized turns out to be an order of magnitude smaller due to the effects of frustration; in this case, the behavior of thermodynamic quantities is analogous, on the whole, to that in two-layer square lattices; a difference manifests itself in the behavior of the gap in the spectrum of quasiparticles in an external magnetic field h. For small fields h, a j-h phase diagram is constructed that determines the domains in which the 120 degrees and the singlet phases exist. It is established that, in the neighborhood of the second-order phase transition, the contribution, to the thermodynamic quantities, of longitudinal spin fluctuations, which are disregarded in the spin-wave description, is comparable to the contribution of transverse fluctuations. (c) 2005 Pleiades Publishing, Inc.
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9.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov A. S., Ovchinnikov S. G.
Заглавие : Density and thermodynamics of hydrogen adsorbed inside narrow carbon nanotubes
Разночтения заглавия :авие SCOPUS: Density and Thermodynamics of Hydrogen Adsorbed Inside Narrow Carbon Nanotubes
Место публикации : Phys. Solid State: AMER INST PHYSICS, 2004. - Vol. 46, Is. 3. - P584-589. - ISSN 1063-7834, DOI 10.1134/1.1687883
Примечания : Cited References: 21. - This study was supported by the federal program “Integration,” project no. Б0017
Предметные рубрики: MOLECULAR-DYNAMICS
TRANSITIONS
TRANSPORT
ENERGY
TUBES
Аннотация: A model is proposed for calculating the thermodynamic functions and the equilibrium density of a one-dimensional chain of molecules (atoms) adsorbed inside a narrow nanotube. The model considers both the interaction between introduced atoms (molecules) and their interaction with the nanotube walls. The quantum-mechanical effects resulting in discrete energy levels of a particle and in its smeared position between neighbors are taken into account. In calculating the free energy at a nonzero temperature, the phonon contribution and the particle transitions to excited levels are considered. The model is applied to calculate the thermodynamic parameters of adsorbed hydrogen molecules inside extremely narrow single-wall carbon nanotubes of the (3,3) and (6,0) type. It is shown that external pressure gives rise to a sequence of first-order phase transitions, which change the density of adsorbed hydrogen molecules. (C) 2004 MAIK "Nauka / Interperiodica".
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10.

Вид документа : Статья из журнала
Шифр издания :
Автор(ы) : Fedorov A. S., Sorokin P. B.
Заглавие : Density and thermodynamics of hydrogen adsorbed on the surface of single-walled carbon nanotubes
Место публикации : Phys. Solid State: MAIK NAUKA/INTERPERIODICA/SPRINGER, 2006. - Vol. 48, Is. 2. - P402-407. - ISSN 1063-7834, DOI 10.1134/S1063783406020351
Примечания : Cited References: 22
Предметные рубрики: MOLECULAR-DYNAMICS
ROOM-TEMPERATURE
STORAGE
ADSORPTION
H-2
TRANSITIONS
TUBES
Аннотация: A method is proposed for calculating the adsorption of hydrogen in single-walled carbon nanotubes. This method involves solving the Schrodinger equation for a particle (hydrogen molecule) moving in a potential generated by the surrounding hydrogen molecules and atoms forming the wall of the carbon nanotube. The interaction potential for hydrogen molecules is taken in the form of the Silvera-Goldman empirical potential, which adequately describes the experimental data on the interaction between H(2) molecules (including the van der Waals interaction). The interaction of hydrogen molecules with carbon atoms is included in the calculation through the Lennard-Jones potential. The free energy at a nonzero temperature is calculated with allowance made for the phonon contribution, which, in turn, makes it possible to take into account the correlations in the mutual arrangement of the neighboring molecules. The dependences of the total energy, the free energy, and the Gibbs thermodynamic potential on the applied pressure P and temperature T are calculated for adsorbed hydrogen molecules. These dependences are obtained for the first time with due regard for the quantum effects. The pressure and temperature dependences of the hydrogen density m(P, T) are also constructed for the first time.
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