3,012 research outputs found
Composite Polarons in Ferromagnetic Narrow-band Metallic Manganese Oxides
A new mechanism is proposed to explain the colossal magnetoresistance and
related phenomena. Moving electrons accompanied by Jahn-Teller phonon and
spin-wave clouds may form composite polarons in ferromagnetic narrow-band
manganites. The ground-state and finite-temperature properties of such
composite polarons are studied in the present paper. By using a variational
method, it is shown that the energy of the system at zero temperature decreases
with the formation of composite polaron; the energy spectrum and effective mass
of the composite polaron at finite temperature is found to be strongly
renormalized by the temperature and the magnetic field. It is suggested that
the composite polaron contribute significantly to the transport and the
thermodynamic properties in ferromagnetic narrow-band metallic manganese
oxides.Comment: Latex, no figur
Global axisymmetric stability analysis for a composite system of two gravitationally coupled scale-free discs
In a composite system of gravitationally coupled stellar and gaseous discs,
we perform linear stability analysis for axisymmetric coplanar perturbations
using the two-fluid formalism. The background stellar and gaseous discs are
taken to be scale-free with all physical variables varying as powers of
cylindrical radius with compatible exponents. The unstable modes set in as
neutral modes or stationary perturbation configurations with angular frequency
.Comment: 7 pages using AAS styl
Monte Carlo Simulations for the Magnetic Phase Diagram of the Double Exchange Hamiltonian
We have used Monte Carlo simulation techniques to obtain the magnetic phase
diagram of the double exchange Hamiltonian. We have found that the Berry's
phase of the hopping amplitude has a negligible effect in the value of the
magnetic critical temperature. To avoid finite size problems in our simulations
we have also developed an approximated expression for the double exchange
energy. This allows us to obtain the critical temperature for the ferromagnetic
to paramagnetic transition more accurately. In our calculations we do not
observe any strange behavior in the kinetic energy, chemical potential or
electron density of states near the magnetic critical temperature. Therefore,
we conclude that other effects, not included in the double exchange
Hamiltonian, are needed to understand the metal-insulator transition which
occurs in the manganites.Comment: 6 pages Revtex, 8 PS figure
Heavy Quarkonium Potential Model and the State of Charmonium
A theoretical explanation of the observed splittings among the P~states of
charmonium is given with the use of a nonsingular potential model for heavy
quarkonia. We also show that the recently observed mass difference between the
center of gravity of the states and the state of
does not provide a direct test of the color hyperfine interaction in heavy
quarkonia. Our theoretical value for the mass of the state is in
agreement with the experimental result, and its E1 transition width is
341.8~keV. The mass of the state is predicted to be 3622.3~MeV.Comment: 15 page REVTEX documen
Extension of ELM suppression window using n=4 RMPs in EAST
The q95 window for Type-I Edge Localized Modes (ELMs) suppression using n=4
even parity Resonant Magnetic Perturbations (RMPs) has been significantly
expanded to a range from 3.9 to 4.8, which is demonstrated to be reliable and
repeatable in EAST over the last two years. This window is significantly wider
than the previous one, which is around q95=3.7pm0.1, and is achieved using n=4
odd parity RMPs. Here, n represents the toroidal mode number of the applied
RMPs and q95 is the safety factor at the 95% normalized poloidal magnetic flux.
During ELM suppression, there is only a slight drop in the stored energy
(<=10%). The comparison of pedestal density profiles suggests that ELM
suppression is achieved when the pedestal gradient is kept lower than a
threshold. This wide q95 window for ELM suppression is consistent with the
prediction made by MARS-F modeling prior to the experiment, in which it is
located at one of the resonant q95 windows for plasma response. The Chirikov
parameter taking into account plasma response near the pedestal top, which
measures the plasma edge stochasticity, significantly increases when q95
exceeds 4, mainly due to denser neighboring rational surfaces. Modeling of
plasma response by the MARS-F code shows a strong coupling between resonant and
non-resonant components across the pedestal region, which is characteristic of
the kink-peeling like response observed during RMP-ELM suppression in previous
studies on EAST. These promising results show the reliability of ELM
suppression using the n=4 RMPs and expand the physical understanding on ELM
suppression mechanism.Comment: 25 pages, 11 figure
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