14,206 research outputs found
A theoretical model of the wave particle interaction of plasma in space
A theoretical model, based on the kinetic theory for the perturbation of plasma in the magnetosphere, is proposed to study the observed disturbances which are caused by both natural and artificial sources that generate wave-like perturbations propagating around the globe. The proposed model covers the wave propagation through a media of transitional (from collisional to collisionless) fully ionized magnetoactive plasma. A systematic formulation of the problem is presented and the method of solution for the transitional model of magnetosphere is discussed. The possible emission of hydromagnetic waves in the magnetosphere during the quiet and disturbed time are also discussed
Multifluids description of dynamics of upper atmosphere
A multifluids model to investigate ionospheric dynamics was established on kinetic theory. Its resultant equations are used to examine the following dynamic problems in the gamma region of 80-2000 Km of the ionosphere: (1) propagation of acoustic modes in the 500-2,000 Km of the ionosphere (two fluid model); (2) the relation between the cross field plasma drift instabilities and type I and type II ionospheric irregularities; and (3) time dependent neutral wind structure and horizontal pressure gradient
Covalency and the metal-insulator transition in titanate and vanadate perovskites
A combination of density functional and dynamical mean-field theory is
applied to the perovskites SrVO, LaTiO and LaVO. We show that
DFT+DMFT in conjunction with the standard fully localized-limit (FLL)
double-counting predicts that LaTiO and LaVO are metals even though
experimentally they are correlation-driven ("Mott") insulators. In addition,
the FLL double counting implies a splitting between oxygen and transition
metal levels which differs from experiment. Introducing into the theory an
\textit{ad hoc} double counting correction which reproduces the experimentally
measured insulating gap leads also to a - splitting consistent with
experiment if the on-site interaction is chosen in a relatively narrow
range ( eV). The results indicate that these early transition
metal oxides will serve as critical test for the formulation of a general
\textit{ab initio} theory of correlated electron metals.Comment: 5 pages, 3 figure
Electronic correlations, magnetism and Hund's rule coupling in the ruthenium perovskites SrRuO and CaRuO
A comparative density functional plus dynamical mean field theory study of
the pseudocubic ruthenate materials CaRuO and SrRuO is presented. Phase
diagrams are determined for both materials as a function of Hubbard repulsion
and Hund's rule coupling . Metallic and insulating phases are found, as
are ferromagnetic and paramagnetic states. The locations of the relevant phase
boundaries are determined. Based on the computed phase diagrams, Mott-dominated
and Hund's dominated regimes of strong correlation are distinguished.
Comparison of calculated properties to experiments indicates that the actual
materials are in the Hund's coupling dominated region of the phase diagram so
can be characterized as Hund's metals, in common with other members of the
ruthenate family. Comparison of the phase diagrams for the two materials
reveals the role played by rotational and tilt (GdFeO-type) distortions of
the ideal perovskite structure. The presence of magnetism in SrRuO and its
absence in CaRuO despite the larger mass and larger tilt/rotational
distortion amplitude of CaRuO can be understood in terms of density of
states effects in the presence of strong Hund's coupling. Comparison of the
calculated low- properties of CaRuO to those of SrRuO provides
insight into the effects of magnetic order on the properties of a Hund's metal.
The study provides a simultaneous description of magnetism and correlations and
explicates the roles played by band theory and Hubbard and Hund's interactions
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