5,469 research outputs found
Spin-excitations of the quantum Hall ferromagnet of composite fermions
The spin-excitations of a fractional quantum Hall system are evaluated within
a bosonization approach. In a first step, we generalize Murthy and Shankar's
Hamiltonian theory of the fractional quantum Hall effect to the case of
composite fermions with an extra discrete degree of freedom. Here, we mainly
investigate the spin degrees of freedom, but the proposed formalism may be
useful also in the study of bilayer quantum-Hall systems, where the layer index
may formally be treated as an isospin. In a second step, we apply a
bosonization scheme, recently developed for the study of the two-dimensional
electron gas, to the interacting composite-fermion Hamiltonian. The dispersion
of the bosons, which represent quasiparticle-quasihole excitations, is
analytically evaluated for fractional quantum Hall systems at \nu = 1/3 and \nu
= 1/5. The finite width of the two-dimensional electron gas is also taken into
account explicitly. In addition, we consider the interacting bosonic model and
calculate the lowest-energy state for two bosons. Besides a continuum
describing scattering states, we find a bound-state of two bosons. This state
is interpreted as a pair excitation, which consists of a skyrmion of composite
fermions and an antiskyrmion of composite fermions. The dispersion relation of
the two-boson state is evaluated for \nu = 1/3 and \nu = 1/5. Finally, we show
that our theory provides the microscopic basis for a phenomenological
non-linear sigma-model for studying the skyrmion of composite fermions.Comment: Revised version, 14 pages, 4 figures, accepted to Phys. Rev.
Analytical results for random walks in the presence of disorder and traps
In this paper, we study the dynamics of a random walker diffusing on a
disordered one-dimensional lattice with random trappings. The distribution of
escape probabilities is computed exactly for any strength of the disorder.
These probabilities do not display any multifractal properties contrary to
previous numerical claims. The explanation for this apparent multifractal
behavior is given, and our conclusion are supported by numerical calculations.
These exact results are exploited to compute the large time asymptotics of the
survival probability (or the density) which is found to decay as . An exact lower bound for the density is found to
decay in a similar way.Comment: 21 pages including 3 PS figures. Submitted to Phys. Rev.
How rare are diffusive rare events?
We study the time until first occurrence, the first-passage time, of rare
density fluctuations in diffusive systems. We approach the problem using a
model consisting of many independent random walkers on a lattice. The existence
of spatial correlations makes this problem analytically intractable. However,
for a mean-field approximation in which the walkers can jump anywhere in the
system, we obtain a simple asymptotic form for the mean first-passage time to
have a given number k of particles at a distinguished site. We show
numerically, and argue heuristically, that for large enough k, the mean-field
results give a good approximation for first-passage times for systems with
nearest-neighbour dynamics, especially for two and higher spatial dimensions.
Finally, we show how the results change when density fluctuations anywhere in
the system, rather than at a specific distinguished site, are considered.Comment: 6 pages, 5 figures. Accepted for publication in Europhysics Letters
(http://www.iop.org/EJ/journal/EPL
Uncertainty Handling in Remote Sensing Data Analysis for Defence
Describes a way of handling uncertainty in IRS imagery by utilising a multivalued recognition system. Roads and bridges can be detected effectively by using the multiple class choices provided by the multivalued recognition system
Uncertainty handling in remote sensing data analysis for defence application
Describes a way of handling uncertainty in IRS imagery by utilising a multivalued recognition system. Roads and bridges can be detected effectively by using the multiple class choices provided by the multivalued recognition system
Sticky Spheres, Entropy barriers and Non-equilibrium phase transitions
A sticky spheres model to describe slow dynamics of a non-equilibrium system
is proposed. The dynamical slowing down is due to the presence of entropy
barriers. We present an exact mean field analysis of the model and demonstrate
that there is a non-equilibrium phase transition from an exponential cluster
size distribution to a powerlaw.Comment: 10pages text and 2 figure
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