499 research outputs found
Estimation of Lyapunov spectra from space-time data
A method to estimate Lyapunov spectra from spatio-temporal data is presented,
which is well-suited to be applied to experimental situations. It allows to
characterize the high-dimensional chaotic states, with possibly a large number
of positive Lyapunov exponents, observed in spatio-temporal chaos. The method
is applied to data from a coupled map lattice
Identifying and modelling delay feedback systems
Systems with delayed feedback can possess chaotic attractors with extremely
high dimension, even if only a few physical degrees of freedom are involved. We
propose a state space reconstruction from time series data of a scalar
observable, coming along with a novel method to identify and model such
systems, if a single variable is fed back. Making use of special properties of
the feedback structure, we can understand the structure of the system by
constructing equivalent equations of motion in spaces with dimensions which can
be much smaller than the dimension of the chaotic attractor. We verify our
method using both numerical and experimental data
Field theoretical analysis of adsorption of polymer chains at surfaces: Critical exponents and Scaling
The process of adsorption on a planar repulsive, "marginal" and attractive
wall of long-flexible polymer chains with excluded volume interactions is
investigated. The performed scaling analysis is based on formal analogy between
the polymer adsorption problem and the equivalent problem of critical phenomena
in the semi-infinite n-vector model (in the limit ) with a
planar boundary. The whole set of surface critical exponents characterizing the
process of adsorption of long-flexible polymer chains at the surface is
obtained. The polymer linear dimensions parallel and perpendicular to the
surface and the corresponding partition functions as well as the behavior of
monomer density profiles and the fraction of adsorbed monomers at the surface
and in the interior are studied on the basis of renormalization group field
theoretical approach directly in d=3 dimensions up to two-loop order for the
semi-infinite n-vector model. The obtained field- theoretical
results at fixed dimensions d=3 are in good agreement with recent Monte Carlo
calculations. Besides, we have performed the scaling analysis of
center-adsorbed star polymer chains with arms of the same length and we
have obtained the set of critical exponents for such system at fixed d=3
dimensions up to two-loop order.Comment: 22 pages, 12 figures, 4 table
Detecting Determinism in High Dimensional Chaotic Systems
A method based upon the statistical evaluation of the differentiability of
the measure along the trajectory is used to identify in high dimensional
systems. The results show that the method is suitable for discriminating
stochastic from deterministic systems even if the dimension of the latter is as
high as 13. The method is shown to succeed in identifying determinism in
electro-encephalogram signals simulated by means of a high dimensional system.Comment: 8 pages (RevTeX 3 style), 5 EPS figures, submitted to Phys. Rev. E
(25 apr 2001
Quantum corrections to the phase diagram of heavy-fermion superconductors
The competition between magnetism and Kondo effect is the main effect
determining the phase diagram of heavy fermion systems. It gives rise to a
quantum critical point which governs the low temperature properties of these
materials. However, experimental results made it clear that a fundamental
ingredient is missing in this description, namely superconductivity. In this
paper we make a step forward in the direction of incorporating
superconductivity and study the mutual effects of this phase and
antiferromagnetism in the phase diagram of heavy fermion metals. Our approach
is based on a Ginzburg-Landau theory describing superconductivity and
antiferromagnetism in a metal with quantum corrections taken into account
through an effective potential. The proximity of an antiferromagnetic
instability extends the region of superconductivity in the phase diagram and
drives this transition into a first order one. On the other hand
superconducting quantum fluctuations near a metallic antiferromagnetic quantum
critical point gives rise to a first order transition from a low moment to a
high moment state in the antiferromagnet. Antiferromagnetism and
superconductivity may both collapse at a quantum bicritical point whose
properties we calculate.Comment: 10 pages, 6 figure
Drinkwater innovaties voor de huishoudelijke eindgebruiker: inventarisatie van praktijkvoorbeelden
KIWA Waterresearch coördineert het Bedrijfstakonderzoek (BTO) voor de drinkwatersector. In het kader van het BTO is de onderzoekslijn Client 21 opgezet, waarbinnen verschillende klantgerelateerde kennisvragen aan bod komen. Toekomstig klantgedrag is één van die kennisvragen. Om inzicht te verkrijgen in toekomstig klantgedrag laat Kiwa Water Research het onderhavige onderzoek ‘gedragspraktijk watergebruik’ uitvoeren, waarvan dit rapport het eerste product i
Effects of degenerate orbitals on the Hubbard model
Stability of a metallic state in the two-orbital Hubbard model at
half-filling is investigated. We clarify how spin and orbital fluctuations are
enhanced to stabilize the formation of quasi-particles by combining dynamical
mean field theory with the quantum Monte Carlo simulations. These analyses shed
some light on the reason why the metallic phase is particularly stable when the
intra- and inter-band Coulomb interactions are nearly equal.Comment: 3 pages, To appear in JPSJ Vol. 72, No. 5 200
Experimental studies on shear connection between steel and lightweight concrete using studs
This contribution describes Standard Push-Out Tests carried out at University of Minho (UM) and the Single Push-Out Tests performed at the Institute of Structural Concrete at RWTH Aachen University using high strength lightweight concrete (HSLWC). The test configuration follows the EC4 recommendations and repeats some dispositions referred by other authors. The experimental studies carried out at RWTH and UM include tests on studs with diameters of 19, 22 and 25 mm and also tests on studs of 19 mm diameter, which are grouped in pairs. The purpose of the experiments conducted is to determine the load-bearing capacity as well as the deformation capacity of commonly used headed shear stud when using high strength lightweight concrete. The results from these tests are compared to those from the tests performed with high strength normal weight concrete (NWC)
Polymers grafted to porous membranes
We study a single flexible chain molecule grafted to a membrane which has
pores of size slightly larger than the monomer size. On both sides of the
membrane there is the same solvent. When this solvent is good, i.e. when the
polymer is described by a self avoiding walk, it can fairly easily penetrate
the membrane, so that the average number of membrane crossings tends, for chain
length , to a positive constant. The average numbers of monomers on
either side of the membrane diverges in this limit, although their ratio
becomes infinite. For a poor solvent, in contrast, the entire polymer is
located, for large , on one side of the membrane. For good and for theta
solvents (ideal polymers) we find scaling laws, whose exponents can in the
latter case be easily understood from the behaviour of random walks.Comment: 4 pages, 6 figure
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