4,252 research outputs found
Relative Periodic Solutions of the Complex Ginzburg-Landau Equation
A method of finding relative periodic orbits for differential equations with
continuous symmetries is described and its utility demonstrated by computing
relative periodic solutions for the one-dimensional complex Ginzburg-Landau
equation (CGLE) with periodic boundary conditions. A relative periodic solution
is a solution that is periodic in time, up to a transformation by an element of
the equation's symmetry group. With the method used, relative periodic
solutions are represented by a space-time Fourier series modified to include
the symmetry group element and are sought as solutions to a system of nonlinear
algebraic equations for the Fourier coefficients, group element, and time
period. The 77 relative periodic solutions found for the CGLE exhibit a wide
variety of temporal dynamics, with the sum of their positive Lyapunov exponents
varying from 5.19 to 60.35 and their unstable dimensions from 3 to 8.
Preliminary work indicates that weighted averages over the collection of
relative periodic solutions accurately approximate the value of several
functionals on typical trajectories.Comment: 32 pages, 12 figure
Coarse Stability and Bifurcation Analysis Using Stochastic Simulators: Kinetic Monte Carlo Examples
We implement a computer-assisted approach that, under appropriate conditions,
allows the bifurcation analysis of the coarse dynamic behavior of microscopic
simulators without requiring the explicit derivation of closed macroscopic
equations for this behavior. The approach is inspired by the so-called
time-step per based numerical bifurcation theory. We illustrate the approach
through the computation of both stable and unstable coarsely invariant states
for Kinetic Monte Carlo models of three simple surface reaction schemes. We
quantify the linearized stability of these coarsely invariant states, perform
pseudo-arclength continuation, detect coarse limit point and coarse Hopf
bifurcations and construct two-parameter bifurcation diagrams.Comment: 26 pages, 5 figure
A Generalized Index for Static Voltage Stability of Unbalanced Polyphase Power Systems including Th\'evenin Equivalents and Polynomial Models
This paper proposes a Voltage Stability Index (VSI) suitable for unbalanced
polyphase power systems. To this end, the grid is represented by a polyphase
multiport network model (i.e., compound hybrid parameters), and the aggregate
behavior of the devices in each node by Th\'evenin Equivalents (TEs) and
Polynomial Models (PMs), respectively. The proposed VSI is a generalization of
the known L-index, which is achieved through the use of compound electrical
parameters, and the incorporation of TEs and PMs into its formal definition.
Notably, the proposed VSI can handle unbalanced polyphase power systems,
explicitly accounts for voltage-dependent behavior (represented by PMs), and is
computationally inexpensive. These features are valuable for the operation of
both transmission and distribution systems. Specifically, the ability to handle
the unbalanced polyphase case is of particular value for distribution systems.
In this context, it is proven that the compound hybrid parameters required for
the calculation of the VSI do exist under practical conditions (i.e., for lossy
grids). The proposed VSI is validated against state-of-the-art methods for
voltage stability assessment using a benchmark system which is based on the
IEEE 34-node feeder
Asymptotics of work distributions in a stochastically driven system
We determine the asymptotic forms of work distributions at arbitrary times
, in a class of driven stochastic systems using a theory developed by Engel
and Nickelsen (EN theory) (arXiv:1102.4505v1 [cond-mat.stat-mech]), which is
based on the contraction principle of large deviation theory. In this paper, we
extend the theory, previously applied in the context of deterministically
driven systems, to a model in which the driving is stochastic. The models we
study are described by overdamped Langevin equations and the work distributions
in the path integral form, are characterised by having quadratic actions. We
first illustrate EN theory, for a deterministically driven system - the
breathing parabola model, and show that within its framework, the Crooks
flucutation theorem manifests itself as a reflection symmetry property of a
certain characteristic polynomial function. We then extend our analysis to a
stochastically driven system, studied in ( arXiv:1212.0704v2
[cond-mat.stat-mech], arXiv:1402.5777v1 [cond-mat.stat-mech]) using a
moment-generating-function method, for both equilibrium and non - equilibrium
steady state initial distributions. In both cases we obtain new analytic
solutions for the asymptotic forms of (dissipated) work distributions at
arbitrary . For dissipated work in the steady state, we compare the large
asymptotic behaviour of our solution to that already obtained in (
arXiv:1402.5777v1 [cond-mat.stat-mech]). In all cases, special emphasis is
placed on the computation of the pre-exponential factor and the results show
excellent agreement with the numerical simulations. Our solutions are exact in
the low noise limit.Comment: 26 pages, 8 figures. Changes from version 1: Several typos and
equations corrected, references added, pictures modified. Version to appear
in EPJ
Stabilization of Unstable Procedures: The Recursive Projection Method
Fixed-point iterative procedures for solving nonlinear parameter dependent problems can converge for some interval of parameter values and diverge as the parameter changes. The Recursive Projection Method (RPM), which stabilizes such procedures by computing a projection onto the unstable subspace is presented. On this subspace a Newton or special Newton iteration is performed, and the fixed-point iteration is used on the complement. As continuation in the parameter proceeds, the projection is efficiently updated, possibly increasing or decreasing the dimension of the unstable subspace. The method is extremely effective when the dimension of the unstable subspace is small compared to the dimension of the system. Convergence proofs are given and pseudo-arclength continuation on the unstable subspace is introduced to allow continuation past folds. Examples are presented for an important application of the RPM in which a âblack-boxâ time integration scheme is stabilized, enabling it to compute unstable steady states. The RPM can also be used to accelerate iterative procedures when slow convergence is due to a few slowly decaying modes
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