1,724 research outputs found
Disorder perturbed Flat Bands I: Level density and Inverse Participation Ratio
We consider the effect of disorder on the tight-binding Hamiltonians with a
flat band and derive a common mathematical formulation of the average density
of states and inverse participation ratio applicable for a wide range of them.
The system information in the formulation appears through a single parameter
which plays an important role in search of the critical points for disorder
driven transitions in flat bands [1]. In weak disorder regime, the formulation
indicates an insensitivity of the statistical measures to disorder strength,
thus confirming the numerical results obtained by our as well as previous
studies.Comment: 34 Pages, 4 figures, Previous version divided in two parts to include
new sections and details, title and abstract changed to
Eigenfunction Statistics of Complex Systems: A Common Mathematical Formulation
We derive a common mathematical formulation for the eigenfunction statistics
of Hermitian operators, represented by a multi-parametric probability density.
The system-information in the formulation enters through two parameters only,
namely, system size and the complexity parameter, a function of all system
parameter including size. The behavior is contrary to the eigenvalue statistics
which is sensitive to complexity parameter only and shows a single parametric
scaling. The existence of a mathematical formulation, of both eigenfunctions
and eigenvalues, common to a wide range of complex systems indicates the
possibility of a similar formulation for many physical properties. This also
suggests the possibility to classify them in various universality classes
defined by complexity parameter.Comment: 16 Figures, Several Changes, Many new sections and figures included,
conclusion slightly change
Level Correlations for Metal-Insulator Transition
We study the level-statistics of a disordered system undergoing the Anderson
type metal-insulator transition. The disordered Hamiltonian is a sparse random
matrix in the site representation and the statistics is obtained by taking an
ensemble of such matrices. It is shown that the transition of levels due to
change of various parameters e.g. disorder, system size, hopping rate can be
mapped to the perturbation driven evolution of the eigenvalues of an ensemble
subjected to Wigner-Dyson type perturbation with an initial state given by a
Poisson ensemble; the mapping is then used to obtain desired
level-correlations.Comment: Latex file, 7 pages, No figure
On the Distribution of zeros of chaotic wavefunction
The wavefunctions in phase-space representation can be expressed as entire
functions of their zeros if the phase space is compact. These zeros seem to
hide a lot of relevant and explicit information about the underlying classical
dynamics. Besides, an understanding of their statistical properties may prove
useful in the analytical calculations of the wavefunctions in quantum chaotic
systems. This motivates us to persue the present study which by a numerical
statistical analysis shows that both long as well as the short range
correlations exist between zeros; while the latter turn out to be universal and
parametric-independent, the former seem to be system dependent and are
significantly affected by various parameters i.e symmetry, localization etc.
Furthermore, for the delocalized quantum dynamics, the distribution of these
zeros seem to mimick that of the zeros of the random functions as well as
random polynomials.Comment: PlainTex, Seven figures (available on direct request to author),
J.Phys. (in Press
Eigenvalue Correlations For Banded Matrices
We study the evolution of the distribution of eigenvalues of
matrix ensembles subject to a change of variances of its matrix elements. Our
results indicate that the evolution of the probability density is governed by a
Fokker- Planck equation similar to the one governing the time-evolution of the
particle- distribution in Wigner-Dyson gas, with relative variances now playing
the role of time. This is also similar to the Fokker-Planck equation for the
distribution of eigenvalues of a matrix subject to a random
perturbation taken from the standard Gaussian ensembles with
perturbation-strength as the "time" variable. This equivalence alonwith the
already known correlations of standard Gaussian ensembles can therefore help us
to obtain the same for various physically-significant cases modeled by random
banded Gaussian ensembles.Comment: Latex file, 5 pages, No figure
Level-Statistics of Disordered Systems: a Single Parametric Formulation
We find that the statistics of levels undergoing metal-insulator transition
in systems with multi-parametric Gaussian disorders behaves in a way similar to
that of the single parametric Brownian ensembles. The latter appear during
aPoisson Wigner-Dyson transition, driven by a random perturbation. The
analogy provides the analytical evidence for the single parameter scaling
behaviour in disordered systems as well as a tool to obtain the
level-correlations at the critical point for a wide range of disorders.Comment: 4 Pages, 4 Figure
Random matrix ensembles with column/row constraints. II
We numerically analyze the random matrix ensembles of real-symmetric matrices
with column/row constraints for many system conditions e.g. disorder type,
matrix-size and basis-connectivity. The results reveal a rich behavior hidden
beneath the spectral statistics and also confirm our analytical predictions,
presented in part I of this paper, about the analogy of their spectral
fluctuations with those of a critical Brownian ensemble which appears between
Poisson and Gaussian orthogonal ensemble.Comment: This is the second part of the replaced version of the article
reference arXiv:1409.6538v
Statistical analysis of chiral structured ensembles: role of matrix constraints
We numerically analyze the statistical properties of complex system with
conditions subjecting the matrix elements to a set of specific constraints
besides symmetry, resulting in various structures in their matrix
representation. Our results reveal an important trend: while the spectral
statistics is strongly sensitive to the number of independent matrix elements,
the eigenfunction statistics seems to be affected only by their relative
strengths. This is contrary to previously held belief of one to one relation
between the statistics of the eigenfunctions and eigenvalues (e.g. associating
Poisson statistics to the localized eigenfunctions and Wigner-Dyson statistics
to delocalized ones).Comment: 23 pages (with double spacing), 7 figure
Criticality in the Quantum Kicked Rotor with a Smooth Potential
We investigate the possibility of an Anderson type transition in the quantum
kicked rotor with a smooth potential due to dynamical localization of the
wavefunctions. Our results show the typical characteristics of a critical
behavior i.e multifractal eigenfunctions and a scale-invariant level-statistics
at a critical kicking strength which classically corresponds to a mixed regime.
This indicates the existence of a localization to delocalization transition in
the quantum kicked rotor.
Our study also reveals the possibility of other type of transitions in the
quantum kicked rotor, with a kicking strength well within strongly chaotic
regime. These transitions, driven by the breaking of exact symmetries e.g.
time-reversal and parity, are similar to weak-localization transitions in
disordered metals.Comment: 15 figures, to be published in Physical review E, 200
Improved Interference in Wireless Sensor Networks
Given a set of sensor node distributed on a 2-dimensional
plane and a source node , the {\it interference problem} deals
with assigning transmission range to each such that the
members in maintain connectivity predicate , and the
maximum/total interference is minimum. We propose algorithm for both {\it
minimizing maximum interference} and {\it minimizing total interference} of the
networks. For minimizing maximum interference we present optimum solution with
running time for connectivity predicate like strong connectivity, broadcast ( is the source), -edge(vertex)
connectivity, spanner, where is the time complexity for
checking the connectivity predicate . The running time of the
previous best known solution was [Bil and
Proietti, 2008].
For the minimizing total interference we propose optimum algorithm for the
connectivity predicate broadcast. The running time of the propose algorithm is
O(n). For the same problem, the previous best known result was -factor approximation algorithm [Bil and Proietti, 2008]. We
also propose a heuristic for minimizing total interference in the case of
strongly connected predicate and compare our result with the best result
available in the literature. Experimental results demonstrate that our
heuristic outperform existing result.Comment: 10 pages, 1 figur
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