13,743 research outputs found
Iterative Splitting Methods: Almost Asymptotic Symplectic Integrator for Stochastic Nonlinear Schr\"odinger Equation
In this paper we present splitting methods which are based on iterative
schemes and applied to stochastic nonlinear Schroedinger equation. We will
design stochastic integrators which almost conserve the symplectic structure.
The idea is based on rewriting an iterative splitting approach as a successive
approximation method based on a contraction mapping principle and that we have
an almost symplectic scheme. We apply a stochastic differential equation, that
we can decouple into a deterministic and stochatic part, while each part can be
solved analytically. Such decompositions allow accelerating the methods and
preserving, under suitable conditions, the symplecticity of the schemes. A
numerical analysis and application to the stochastic Schroedinger equation are
presented.Comment: 17 page
Numerical Methods of the Maxwell-Stefan Diffusion Equations and Applications in Plasma and Particle Transport
In this paper, we present a model based on a local thermodynamic equilibrium,
weakly ionized plasma-mixture model used for medical and technical applications
in etching processes. We consider a simplified model based on the
Maxwell-Stefan model, which describe multicomponent diffusive fluxes in the gas
mixture. Based on additional conditions to the fluxes, we obtain an irreducible
and quasi-positive diffusion matrix. Such problems results into nonlinear
diffusion equations, which are more delicate to solve as standard diffusion
equations with Fickian's approach. We propose explicit time-discretisation
methods embedded to iterative solvers for the nonlinearities. Such a
combination allows to solve the delicate nonlinear differential equations more
effective. We present some first ternary component gaseous mixtures and discuss
the numerical methods.Comment: 1
Iterative Splitting Methods for Coulomb Collisions in Plasma Simulations
In this paper, we present splitting methods that are based on iterative
schemes and applied to plasma simulations. The motivation arose of solving the
Coulomb collisions, which are modeled by nonlinear stochastic differential
equations. We apply Langevin equations to model the characteristics of the
collisions and we obtain coupled nonlinear stochastic differential equations,
which are delicate to solve. We propose well-known deterministic splitting
schemes that can be extended to stochastic splitting schemes, by taking into
account the stochastic behavior. The benefit decomposing the different equation
parts and solve such parts individual is taken into account in the analysis of
the new iterative splitting schemes. Numerical analysis and application to
various Coulomb collisions in plasma applications are presented.Comment: 27 page
Simulation of a Heat Transfer in Porous Media
We are motivated to model a heat transfer to a multiple layer regime and
their optimization for heat energy resources. Such a problem can be modeled by
a porous media with different phases (liquid and solid).
The idea arose of a geothermal energy reservoir which can be used by cities,
e.g. Berlin.
While hot ground areas are covered to most high populated cites, the energy
resources are important and a shift to use such resources are enormous.
We design a model of the heat transport via the flow of water through the
heterogeneous layer of the underlying earth sediments.
We discuss a multiple layer model, based on mobile and immobile zones.
Such numerical simulations help to economize on expensive physical
experiments and obtain control mechanisms for the delicate heating process.Comment: 2
Recent Spectroscopy Results from ZEUS
Recent results on light hadron spectroscopy are reported, with special
emphasis on the evidence for a narrow baryonic state decaying to Ks p and Ks
pbar, compatible with the pentaquark state theta^+ observed by fixed target
experiments. The data were collected with the ZEUS detector at HERA using an
integrated luminosity of 121 pb^-1. The analyses were performed in the central
rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass
energy of 300-318 GeV. Evidence for a narrow resonance in the Ks p and Ks pbar
invariant mass spectrum is obtained, with mass 1521.5 \pm
1.5(stat)^{+2.8}_{-1.7}(syst) and width consistent with the experimental
resolution. If the Ks p part of the signal is identified with the strange
pentaquark theta^+, the Ks pbar part is the first evidence for its
antiparticle, thetabar^-. Supporting results on other light hadron resonances
are also discussed.Comment: To appear in the proceedings of 39th Rencontres de Moriond on QCD and
High-Energy Hadronic Interactions, La Thuile, Italy, 28 Mar - 4 Apr 200
Embedded Zassenhaus Expansion to Operator Splitting Schemes: Theory and Application in Fluid Dynamics
In this paper, we contribute operator-splitting methods improved by the
Zassenhaus product for the numerical solution of linear partial differential
equations. We address iterative splitting methods, that can be improved by
means of the Zassenhaus product formula, which is a sequnential splitting
scheme. The coupling of iterative and sequential splitting techniques are
discussed and can be combined with respect to their compuational time. While
the iterative splitting schemes are cheap to compute, the Zassenhaus product
formula is more expensive, based on the commutators but achieves higher order
accuracy. Iterative splitting schemes and also Zassenhaus products are applied
in physics and physical chemistry are important and are predestinated to their
combinations of each benefits. Here we consider phase models in CFD
(computational fluid dynamics). We present an underlying analysis for obtaining
higher order operator-splitting methods based on the Zassenhaus product.
Computational benefits are given with sparse matrices, which arose of spatial
discretization of the underlying partial differential equations. While
Zassenhaus formula allows higher accuracy, due to the fact that we obtain
higher order commutators, we combine such an improved initialization process to
cheap computable to linear convergent iterative splitting schemes.
Theoretical discussion about convergence and application examples are
discussed with CFD problems.Comment: 17 page
Multiscale methods for Levitron Problems: Theory and Applications
In this paper, we describe a multiscale model based on magneto-static traps
of neutral atoms or ion traps. The idea is to levitate a magnetic spinning top
in the air repelled by a base magnet.
For such a problem, we have to deal with different time and spatial scales
and we propose a novel splitting method for solving the levitron problem.
We focus on the multiscale problem, which we obtain by coupling the kinetic T
and the potential U part of our equation. The kinetic and potential parts, can
be seen as generators of flows.
The main problem is based on the accurate computation of the Hamiltonian
equation and we propose a novel higher order splitting scheme to obtain stable
states near the relative equilibrium. To improve the splitting scheme we apply
a novel method so called MPE (multiproduct expansion method), which include
higher order extrapolation schemes.
In numerical studies, we discuss the stability near this relative equilibrium
with our improved time-integrators. Best results are obtained by iterative and
extrapolated Verlet schemes in comparison to higher order explicit Runge-Kutta
schemes. Experiments are applied to a magnetic top in an axisymmetric magnetic
field (i.e. the Levitron) and we discuss the future applications to quantum
computations.Comment: 12 pages, 6 figure
Iterative operator-splitting methods for unbounded operators: Error analysis and examples
In this paper we describe an iterative operator-splitting method for
unbounded operators. We derive error bounds for iterative splitting methods in
the presence of unbounded operators and semigroup operators. Here mixed
applications of hyperbolic and parabolic type are allowed and discussed in the
applications. Mixed experiments are applied to ordinary differential equations
and evolutionary Schr\"odinger equations.Comment: 16 Page
Iterative Implicit Methods for Solving Hodgkin-Huxley Type Systems
We are motivated to approximate solutions of a Hodgkin-Huxley type model with
implicit methods. As a representative we chose a psychiatric disease model
containing stable as well as chaotic cycling behaviour. We analyze the
bifurcation pattern and show that some implicit methods help to preserve the
limit cycles of such systems. Further, we applied adaptive time stepping for
the solvers to boost the accuracy, allowing us a preliminary zoom into the
chaotic area of the system.Comment: 25 pages, 8 figures, 3 table
Comparison of Integrators for Electromagnetic Particle in Cell Methods: Algorithms and Applications
In this paper, we present different types of integrators for electro-magnetic
particle-in-cell (PIC) methods. While the integrator is an important tool of
the PIC methods, it is necessary to characterize the different conservation
approaches of the integrators, e.g. symplecticity, energy- or
charge-conservation. We discuss the different principles, e.g. composition,
filtering, explicit and implicit ideas.
While, particle in cell methods are well-studied, the combination between the
different parts, i.e. pusher, solver and approximations are hardly to analyze.
we concentrate on choosing the optimal pusher component, with respect to
conservation and convergence behavior.
We discuss oscillations of the pusher component, strong external magnetic
fields and optimal conservation of energy and momentum.
The algorithmic ideas are discussed and numerical experiments compare the
exactness of the different schemes.
An outlook to overcome the different error components is discussed in the
future works.Comment: 23 page
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