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 $|\phi|^4$ n-vector model (in the limit $n\to 0$) 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 $|\phi|^4$ 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 $f$ 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 $N\to\infty$, 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 $N$, 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