5,330 research outputs found
Ferromagnetic ground state of an orbital degenerate electronic model for transition-metal oxides: exact solution and physical mechanism
We present an exact ground state solution of a one-dimensional electronic
model for transition-metal oxides in the strong coupling limit. The model
contains doubly degenerated orbit for itinerant electrons and the Hund coupling
between the itinerant electrons and localized spins. The ground state is proven
to be a full ferromagnet for any density of electrons. Our model provides a
rigorous example for metallic ferromagnetism in narrow band systems. The
physical mechanism for ferromagnetism and its relevance to high-dimensional
systems, like RXMnO, are discussed. Due to the orbital
degeneracy of itinerant electrons, the superexchange coupling can be
ferromagnetic rather than antiferromagnetic in the one-band case.Comment: 4 page, no figure To appear in Phys. Rev. B, (January 1, 1999
An effective Hamiltonian for an extended Kondo lattice model and a possible origin of charge ordering in half-doped manganites
An effective Hamiltonian is derived in the case of the strong Hund coupling
and on-site Coulomb interaction by means of a projective perturbation approach.
A physical mechanism for charge ordering in half-doped manganites
(R_{0.5}X_{0.5}MnO_3) is proposed. The virtual process of electron hopping
results in antiferromagnetic superexchange and a repulsive interaction, which
may drive electrons to form a Wigner lattice. The phase diagram of the ground
state of the model is presented at half doping. In the case of formation of
Wigner lattice, we prove that spins of electrons are aligned ferromagnetically
as well as that the localized spin background is antiferromagnetic. The
influence of the on-site Coulomb interaction is also discussed.Comment: 6 pages ReTex with two figures To appear in Phys. Rev. B 59, (June 1,
1999
Application of a simplified probe feed impedance formula to the design of a dual frequency patch antenna
A simplified probe feed input impedance for a rectangular patch antenna based on the Green's function is used to design a dual frequency matched antenna. The predicted results at design frequencies of 1.9 and 2.4 GHz are in close agreement with experimental measurements
Formation of superheavy nuclei in cold fusion reactions
Within the concept of the dinuclear system (DNS), a dynamical model is
proposed for describing the formation of superheavy nuclei in complete fusion
reactions by incorporating the coupling of the relative motion to the nucleon
transfer process. The capture of two heavy colliding nuclei, the formation of
the compound nucleus and the de-excitation process are calculated by using an
empirical coupled channel model, solving a master equation numerically and
applying statistical theory, respectively. Evaporation residue excitation
functions in cold fusion reactions are investigated systematically and compared
with available experimental data. Maximal production cross sections of
superheavy nuclei in cold fusion reactions with stable neutron-rich projectiles
are obtained. Isotopic trends in the production of the superheavy elements
Z=110, 112, 114, 116, 118 and 120 are analyzed systematically. Optimal
combinations and the corresponding excitation energies are proposed.Comment: 18 pages, 8 figure
News on PHOTOS Monte Carlo: gamma^* -> pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma)
PHOTOS Monte Carlo is widely used for simulating QED effects in decay of
intermediate particles and resonances. It can be easily connected to other main
process generators. In this paper we consider decaying processes gamma^* ->
pi^+ pi^-(gamma) and K^\pm -> pi^+ pi^- e^\pm nu (gamma) in the framework of
Scalar QED. These two processes are interesting not only for the technical
aspect of PHOTOS Monte Carlo, but also for precision measurement of
alpha_{QED}(M_Z), g-2, as well as pi pi scattering lengths.Comment: 6 pages, 11 figures, proceedings of the PhiPsi09, Oct. 13-16, 2009,
Beijing, Chin
Comment on 'Note on the dog-and-rabbit chase problem in introductory kinematics'
We comment on the recent paper by Yuan Qing-Xin and Du Yin-Xiao (Eur. J.
Phys. 29 (2008) N43-N45).Comment: 2 pages, no figure
Possible Way to Synthesize Superheavy Element Z=117
Within the framework of the dinuclear system model, the production of
superheavy element Z=117 in possible projectile-target combinations is analyzed
systematically. The calculated results show that the production cross sections
are strongly dependent on the reaction systems. Optimal combinations,
corresponding excitation energies and evaporation channels are proposed in this
letter, such as the isotopes ^{248,249}Bk in ^{48}Ca induced reactions in 3n
evaporation channels and the reactions ^{45}Sc+^{246,248}Cm in 3n and 4n
channels, and the system ^{51}V+^{244}Pu in 3n channel.Comment: 10 pages, 4 figures, 1 tabl
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