259 research outputs found
Order parameters in the Verwey phase transition
The Verwey phase transition in magnetite is analyzed on the basis of the
Landau theory. The free energy functional is expanded in a series of components
belonging to the primary and secondary order parameters. A low-temperature
phase with the monoclinic P2/c symmetry is a result of condensation of two
order parameters X_3 and \Delta_5 . The temperature dependence of the shear
elastic constant C_44 is derived and the mechanism of its softening is
discussed.Comment: 4 pages, 1 figur
Comparative study of the electronic structures of Fe3O4 and Fe2SiO4
The electronic properties of two spinels FeO and FeSiO are
studied by the density functional theory. The local Coulomb repulsion and
the Hund's exchange between the electrons on iron are included. For
, both spinels are half-metals, with the minority states at the
Fermi level. Magnetite remains a metal in a cubic phase even at large values of
. The metal-insulator transition is induced by the phonon, which
lowers the total energy and stabilizes the charge-orbital ordering.
FeSiO transforms to a Mott insulating state for eV with a gap
. The antiferromagnetic interactions induce the tetragonal
distortion, which releases the geometrical frustration and stabilizes the
long-range order. The differences of electronic structures in the high-symmetry
cubic phases and the distorted low-symmetry phases of both spinels are
discussed.Comment: 6 pages, 6 figure
Nucleation Processes in Incommensurate Phases
The commensurate-incommensurate phase transition in crystals in driven by the nuclei called stripples. The stripple has a structure defined by the symmetries of crystal phases. It is nucleated as a result of thermal fluctuations. Since a macroscopic number of stripples is needed to complete the phase transition a collective nucleation can take place. There are two ideal mechaniscms of collective stripple nucleations : cascade and serial ones. The stripple appearences are illustrated by the results of mocelular-dynamics simulation on the model systems
Взаимосвязь инвестиционной политики предприятия с повышением качества и эффективности управления
В современных условиях для эффективной деятельности предприятия особенно актуальной является проблема мобилизации и эффективного использования инвестиций. Инвестиции является неотъемлемой частью деловой активности субъектов хозяйствования, в том числе производственной, инновационной, рыночной, маркетинговой и иной деятельности.
Целью данной работы является: изучить теоретические аспекты инвестиций; рассмотреть методологические подходы к оценке эффективности инвестиций; исследовать систему управления инвестиционной деятельностью предприятий; изучить понятие эффективности предприятия; провести анализ инвестиционной деятельности предприятия ООО "Потенциал" провести оценку влияния инвестиций на эффективность деятельности предприятия ООО "Потенциал"In modern conditions, for the efficient operation of an enterprise, the problem of mobilization and efficient use of investments is especially urgent. Investment is an integral part of the business activity of business entities, including production, innovation, market, marketing and other activities.
The aim of this work is: to study the theoretical aspects of investment; consider methodological approaches to assessing the effectiveness of investments; explore the system of investment management of enterprises; to study the concept of enterprise efficiency; to analyze the investment activity of the enterprise LLC “Potential” to assess the impact of investments on the efficiency of the enterprise LLC “Potential
Basal-plane Incommensurate Phases in HCP Structures
An Ising model with competing interaction is used to study the appearance of
incommensurate phases in the basal plane of an hexagonal closed-packed
structure. The calculated mean-field phase diagram reveals various
1q-incommensurate and lock-in phases. The results are applied to explain the
basal-plane incommensurate phase in some compounds of the A'A"BX_4 family, like
K_2MoO_4, K_2WO_4, Rb_2WO4 and to describe the sequence of high-temperature
phase transitions in other compounds of this family.Comment: 8 pages, RevTeX + 4 ps figure
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