132 research outputs found
Impacts of magnetic permeability on electromagnetic data collected in settings with steel-cased wells
Electromagnetic methods are increasingly being applied in settings with steel
infrastructure. These include applications such as monitoring of CO2
sequestration or even assessing the integrity of a wellbore. In this paper, we
examine the impacts of the magnetic permeability of a steel-cased well on
electromagnetic responses in grounded source experiments. We consider a
vertical wellbore and simulate time and frequency domain data on 3D cylindrical
meshes. Permeability slows the decay of surface electric fields in the time
domain and contributes to a phase shift in the frequency domain. We develop our
understanding of how permeability alters currents within, and external to, the
casing by focussing first on the time domain response and translating insights
to the frequency domain. Following others, we rewrite Maxwell's equations to
separate the response into terms that describe the magnetization and induction
effects. Magnetic permeability impacts the responses in two ways: (1) it
enhances the inductive component of the response in the casing, and (2) it
creates a magnetization current on the outer wall of the casing. The
interaction of these two effects results in a poloidal current system within
the casing. It also generates anomalous currents external to the casing that
can alter the geometry and magnitude of currents in the surrounding geologic
formation. This has the potential to be advantageous for enhancing responses in
monitoring applications
Intermittency transitions to strange nonchaotic attractors in a quasiperiodically driven Duffing oscillator
Different mechanisms for the creation of strange nonchaotic attractors (SNAs)
are studied in a two-frequency parametrically driven Duffing oscillator. We
focus on intermittency transitions in particular, and show that SNAs in this
system are created through quasiperiodic saddle-node bifurcations (Type-I
intermittency) as well as through a quasiperiodic subharmonic bifurcation
(Type-III intermittency). The intermittent attractors are characterized via a
number of Lyapunov measures including the behavior of the largest nontrivial
Lyapunov exponent and its variance as well as through distributions of
finite-time Lyapunov exponents. These attractors are ubiquitous in
quasiperiodically driven systems; the regions of occurrence of various SNAs are
identified in a phase diagram of the Duffing system.Comment: 24 pages, RevTeX 4, 12 EPS figure
Synchronization and directed percolation in coupled map lattices
We study a synchronization mechanism, based on one-way coupling of
all-or-nothing type, applied to coupled map lattices with several different
local rules. By analyzing the metric and the topological distance between the
two systems, we found two different regimes: a strong chaos phase in which the
transition has a directed percolation character and a weak chaos phase in which
the synchronization transition occurs abruptly. We are able to derive some
analytical approximations for the location of the transition point and the
critical properties of the system.
We propose to use the characteristics of this transition as indicators of the
spatial propagation of chaoticity.Comment: 12 pages + 12 figure
Synchronisation in Coupled Sine Circle Maps
We study the spatially synchronized and temporally periodic solutions of a
1-d lattice of coupled sine circle maps. We carry out an analytic stability
analysis of this spatially synchronized and temporally periodic case and obtain
the stability matrix in a neat block diagonal form. We find spatially
synchronized behaviour over a substantial range of parameter space. We have
also extended the analysis to higher spatial periods with similar results.
Numerical simulations for various temporal periods of the synchronized
solution, reveal that the entire structure of the Arnold tongues and the
devil's staircase seen in the case of the single circle map can also be
observed for the synchronized coupled sine circle map lattice. Our formalism
should be useful in the study of spatially periodic behaviour in other coupled
map lattices.Comment: uuencoded, 1 rextex file 14 pages, 3 postscript figure
Fundamental scaling laws of on-off intermittency in a stochastically driven dissipative pattern forming system
Noise driven electroconvection in sandwich cells of nematic liquid crystals
exhibits on-off intermittent behaviour at the onset of the instability. We
study laser scattering of convection rolls to characterize the wavelengths and
the trajectories of the stochastic amplitudes of the intermittent structures.
The pattern wavelengths and the statistics of these trajectories are in
quantitative agreement with simulations of the linearized electrohydrodynamic
equations. The fundamental distribution law for the durations
of laminar phases as well as the power law of the amplitude distribution
of intermittent bursts are confirmed in the experiments. Power spectral
densities of the experimental and numerically simulated trajectories are
discussed.Comment: 20 pages and 17 figure
Superconducting states and depinning transitions of Josephson ladders
We present analytical and numerical studies of pinned superconducting states
of open-ended Josephson ladder arrays, neglecting inductances but taking edge
effects into account. Treating the edge effects perturbatively, we find
analytical approximations for three of these superconducting states -- the
no-vortex, fully-frustrated and single-vortex states -- as functions of the dc
bias current and the frustration . Bifurcation theory is used to derive
formulas for the depinning currents and critical frustrations at which the
superconducting states disappear or lose dynamical stability as and are
varied. These results are combined to yield a zero-temperature stability
diagram of the system with respect to and . To highlight the effects of
the edges, we compare this dynamical stability diagram to the thermodynamic
phase diagram for the infinite system where edges have been neglected. We
briefly indicate how to extend our methods to include self-inductances.Comment: RevTeX, 22 pages, 17 figures included; Errata added, 1 page, 1
corrected figur
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