817 research outputs found
Thermodynamics of the Fermi gas in a nanotube
For the ideal Fermi gas that fills the space inside a cylindrical tube, there
are calculated the thermodynamic characteristics in general form for arbitrary
temperatures, namely: the thermodynamic potential, energy, entropy, equations
of state, heat capacities and compressibilities. All these quantities are
expressed through the introduced standard functions and their derivatives. The
radius of the tube is considered as an additional thermodynamic variable. It is
shown that at low temperatures in the quasi-one-dimensional case the
temperature dependencies of the entropy and heat capacities remain linear. The
dependencies of the entropy and heat capacities on the chemical potential have
sharp maximums at the points where the filling of a new discrete level begins.
The character of dependencies of thermodynamic quantities on the tube radius
proves to be qualitatively different in the cases of fixed linear and fixed
total density. At the fixed linear density these dependencies are monotonous
and at the fixed total density they have an oscillating character. Key words:
Fermi particle, nanotube, thermodynamic functions, low-dimensional systems,
equation of state, heat capacity, compressibilityComment: 12 pages, 9 figures. arXiv admin note: substantial text overlap with
arXiv:1608.0720
The equation of state and the quasiparticle mass in the degenerate Fermi system with an effective interaction
General formulas are derived for the quasiparticle effective mass and the
equation of state of the Fermi system with account of the interparticle
attraction at long distances and repulsion at short distances. Calculations are
carried out of the equation of state and the effective mass of the Fermi system
at zero temperature with the use of the modified Morse potential. It is shown
that the pair repulsive forces promote a decrease of the effective mass, and
the attractive forces promote its increase. With a certain choice of the
parameters of the potential the dependence of the pressure on the density has a
nonmonotonic character, which enables to describe the coexistence of the liquid
and gaseous phases. The influence of three-body interactions on the equation of
state and the effective mass is considered. The calculation results are
compared with experimental data concerning the quasiparticle effective mass in
the liquid He.
Key words: normal Fermi liquid, effective mass, quasiparticle, equation of
state, interaction potentialComment: 10 pages, 3 figure
The self-consistent field model for Fermi systems with account of three-body interactions
On the basis of a microscopic model of self-consistent field, the
thermodynamics of the many-particle Fermi system at finite temperatures with
account of three-body interactions is built and the quasiparticle equations of
motion are obtained. It is shown that the delta-like three-body interaction
gives no contribution into the self-consistent field, and the description of
three-body forces requires their nonlocality to be taken into account. The
spatially uniform system is considered in detail, and on the basis of the
developed microscopic approach general formulas are derived for the fermion's
effective mass and the system's equation of state with account of contribution
from three-body forces. The effective mass and pressure are numerically
calculated for the potential of "semi-transparent sphere" type at zero
temperature. Expansions of the effective mass and pressure in powers of density
are obtained. It is shown that, with account of only pair forces, the
interaction of repulsive character reduces the quasiparticle effective mass
relative to the mass of a free particle, and the attractive interaction raises
the effective mass. The question of thermodynamic stability of the Fermi system
is considered and the three-body repulsive interaction is shown to extend the
region of stability of the system with the interparticle pair attraction. The
quasiparticle energy spectrum is calculated with account of three-body forces.Comment: 21 pages, 5 figure
Degenerate Odd Poisson Bracket on Grassmann Variables
A linear degenerate odd Poisson bracket (antibracket) realized solely on
Grassmann variables is presented. It is revealed that this bracket has at once
three nilpotent -like differential operators of the first, the second
and the third orders with respect to the Grassmann derivatives. It is shown
that these -like operators together with the Grassmann-odd nilpotent
Casimir function of this bracket form a finite-dimensional Lie superalgebra.Comment: 5 pages, LATEX. Corrections of misprints. The relation (23) is adde
Phonon and optical-roton branches of excitations of the Bose system
For a system of a large number of Bose particles, a chain of coupled
equations for the averages of field operators is obtained. In the approximation
where only the averages of one field operator and the averages of products of
two operators at zero temperature are taken into account, there is derived a
closed system of dynamic equations. Taking into account the finite range of the
interaction potential between particles, the spectrum of elementary excitations
of a many-particle Bose system is calculated, and it is shown that it has two
branches: a sound branch and an optical branch with an energy gap at zero
momentum. At high density, both branches are nonmonotonic and have the
roton-like minima. The dispersion of the phonon part of the spectrum is
considered. The performed calculations and analysis of experiments on neutron
scattering allow to make a statement about the complex structure of the Landau
dispersion curve in the superfluid He-4.Comment: 18 pages, 6 figure
Spin Seebeck effect in Y-type hexagonal ferrite thin films
Spin Seebeck effect (SSE) has been investigated in thin films of two
Y-hexagonal ferrites BaZnFeO (Zn2Y) and
BaCoFeO (Co2Y) deposited by a spin-coating method on
SrTiO(111) substrate. The selected hexagonal ferrites are both
ferrimagnetic with similar magnetic moments at room temperature and both
exhibit easy magnetization plane normal to -axis. Despite that, SSE signal
was only observed for Zn2Y, whereas no significant SSE signal was detected for
Co2Y. We tentatively explain this different behavior by a presence of two
different magnetic ions in Co2Y, whose random distribution over octahedral
sites interferes the long range ordering and enhances the Gilbert damping
constant. The temperature dependence of SSE for Zn2Y was measured and analyzed
with regard to the heat flux and temperature gradient relevant to the SSE
signal.Comment: 7 pages, 9 figure
Управління міграційним потенціалом на сучасному етапі
В доповіді розглянуто питання щодо сутності міграційного потенціалу населення та ключових факторів його формування в сучасних умовах. Обґрунтовано необхідність управління ним для збереження людського потенціалу держави.В докладе рассмотрен вопрос о сущности миграционного потенциала населения и ключевых факторов его формирования в современных условиях. Обоснована необходимость управления им для сохранения человеческого потенциала государства.The report examined the question of the nature of the migration potential and the key factors of its formation in the modern world. The need for the management of the migration potential is justified for the preservation of human potential of the state.
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