414 research outputs found
Screened Interaction and Self-Energy in an Infinitesimally Polarized Electron Gas via the Kukkonen-Overhauser Method
The screened electron-electron interaction and the
electron self-energy in an infinitesimally polarized electron gas are derived
by extending the approach of Kukkonen and Overhauser. Various quantities in the
expression for are identified in terms of the relevant
response functions of the electron gas. The self-energy is obtained from
by making use of the GW method which in this case
represents a consistent approximation. Contact with previous calculations is
made.Comment: 7 page
Study of supersolidity in the two-dimensional Hubbard-Holstein model
We derive an effective Hamiltonian for the two-dimensional Hubbard-Holstein
model in the regimes of strong electron-electron and strong electron-phonon
interactions by using a nonperturbative approach. In the parameter region where
the system manifests the existence of a correlated singlet phase, the effective
Hamiltonian transforms to a Hamiltonian for hard-core-bosons
on a checkerboard lattice. We employ quantum Monte Carlo simulations, involving
stochastic-series-expansion technique, to obtain the ground state phase
diagram. At filling , as the strength of off-site repulsion increases, the
system undergoes a first-order transition from a superfluid to a diagonal
striped solid with ordering wavevector or
. Unlike the one-dimensional situation, our results in the
two-dimensional case reveal a supersolid phase (corresponding to the diagonal
striped solid) around filling and at large off-site repulsions.
Furthermore, for small off-site repulsions, we witness a valence bond solid at
one-fourth filling and tiny phase-separated regions at slightly higher
fillings.Comment: Accepted in EPJ
Mean-Field Approach to Charge, Orbital, and Spin Ordering in Manganites
We present a mean-field theory of charge, orbital, and spin ordering in
manganites at 50% and 0% dopings by considering Jahn-Teller interaction,
nearest-neighbor repulsion, and no single-site double occupancy. For spinless
fermions, we show that Jahn-Teller distortion and charge-orbital ordering occur
simultaneously. In our two-dimensional model at 50% doping, for small
nearest-neighbor repulsion the system is orbitally polarized while for larger
repulsion the system undergoes CE type ordering. As for the 0% doping case, the
ground state is orbitally antiferromagnetic. Upon including spin degree of
freedom, at both 50% and 0% dopings the ordering remains the same at small
antiferromagnetic coupling between adjacent core spins.Comment: 4 pages, 3 figure
Pseudo-gap and spin polarization in a two-dimensional electron gas
Tunnelling density of states in the vicinity of Fermi level of a
two-dimensional electron gas subjected to an external parallel and zeroth
magnetic field is calculated. It reveals a pseudo-gap recently observed in the
experiments. The gap originates in spin polarization of 2DEG. Non-monotonic
dependence of energy on a Landau level filling factor (density) was obtained.
It implies the tunneling current peculiarities at filling factors 1/2 and 1.
The Ising-like model of the exchange interaction in 2DEG was exploited instead
of the conventional one. It was crucial to achieve even a qualitative agreement
with experimental data.Comment: 6 pages, 3 figure; corrected typos, improved figure
Analytical expressions for the charge-charge local-field factor and the exchange-correlation kernel of a two-dimensional electron gas
We present an analytical expression for the static many-body local field
factor of a homogeneous two-dimensional electron gas, which
reproduces Diffusion Monte Carlo data and embodies the exact asymptotic
behaviors at both small and large wave number . This allows us to also
provide a closed-form expression for the exchange and correlation kernel
, which represents a key input for density functional studies of
inhomogeneous systems.Comment: 5 pages, 3 figure
Calibration and accuracy determination of airdata system for a modern fighter
An Air data system (ADS) is an essential avionics module found in modern fighter
aircraft cockpits. It provides critical information about the aircraft to the pilot throughout
the flight regime. Airdata system comprises of air data computer and their associated
sensors. Sensors instrumented on aircraft normally measure pressures and flow angles in the
local flow field using vanes and probes. However, aircraft requires the free stream
parameters for flying. Therefore, forward lookup tables in Air Data Computer (ADC) are
used to covert local parameters measured using airdata sensor to free stream parameters. In
order to design flight controls, improved system performance, ADS should deliver accurate
output. Accuracy of free stream parameters depends upon the accuracy of these tables in Air
data computer. In this paper, the airdata system of a modern fighter aircraft is considered.
This system carries airdata tables which are calibrated/updated using Maximum Likelihood
Estimation (MLE) method. The accuracy of it needs to be determined by another
independent technique. Hence an Extended Kalman Filter (EKF) is proposed to calibrate
and describe the accuracy limits of airdata system. The technique is tested with flight data
and the results demonstrate the strength of the technique for airdata calibration and
accuracy determination
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