Udo Schwarz - Academia.edu (original) (raw)

Papers by Udo Schwarz

Research paper thumbnail of Measures of complexity in signal analysis

AIP Conference Proceedings, 1996

Research paper thumbnail of Reconstruction of grand minima of solar activity from Delta 14 C data - Linear and nonlinear signal analysis

Research paper thumbnail of Reconstruction of grand minima of solar activity from A14C data' Linear and nonlinear signal analysis

Journal of Geophysical Research, 1996

Research paper thumbnail of Non-linear data analysis and statistical techniques in solar radio astronomy

Lecture Notes in Physics, 1995

Research paper thumbnail of Application of Nonlinear Techniques to SS CYG

Research paper thumbnail of The Earth' magnetic field in the last 100 kyr

Rock-magnetic and palaeo-magnetic data from sediments of two Italian lakes provide a reconstructi... more Rock-magnetic and palaeo-magnetic data from sediments of two Italian lakes provide a reconstruction of the Earth' magnetic field in the last 100 kyr. Since the measurements contain also the climate signal, we apply the Independent Component Analysis in order to extract the signal of the Earth' magnetic field.

Research paper thumbnail of Evalutionsbericht des Interdisziplinaren Zentrums fur Dynamik komplexer Systeme (DYKOS)

Research paper thumbnail of On Nonlinear Signal Processing

Research paper thumbnail of Stochastics In Circumplanetary Dust Dynamics

Charged dust grains in circumplanetary environments experience, beyond various de- terministic fo... more Charged dust grains in circumplanetary environments experience, beyond various de- terministic forces, also stochastic perturbations: E.g., fluctuations of the magnetic field, the charge of the grains etc. Here, we investigate the dynamics of a dust population in a circular orbit around the planet which is perturbed by a stochastic magnetic field B , modeled by an isotropi- cally Gaussian white noise. The resulting perturbation equations give rise to a modi- 2 fied diffusion of the inclinations and eccentricities ­ x D [t +/- sin[2nt]/(2n)] (x - alias for eccentricity e and the inclination i, t - time). The diffusion coefficient is found to be D = [G]2/n, where the gyrofrequency and the orbital frequency are denoted by G, and n, respectively. This behavior has been checked by numerical experiments. We have chosen dust grains (1µm in radius) initially moving in circular orbits around a planet (Jupiter) and integrated numerically their trajectories over their typical lifetimes (100 ye...

Research paper thumbnail of Statistical Parameters of a Control Strategy of Laser Beam Melt

Laser beam melt ablation - a contact-free machining process - oers several advantages compared to... more Laser beam melt ablation - a contact-free machining process - oers several advantages compared to conventional processing mechanisms: there exists no tool wear and even extremely hard or brittle materials can be processed. During ablation the workpiece is molten by a CO2-laser beam, this melt is then driven out by the impulse of a process gas. The idea behind laser ablation is rather simple, but it has a major limitation in practical applications: with increasing ablation rates surface quality of the workpiece processed declines rapidly. At high ablation rates, depending on the process parameters dierent periodic-like structures can be observed on the ablated surface. These structures show a dependence on the line energy, which has been identi ed as a fundamental control parameter. In dependence on this parameter several regimes with dierent behaviours of the process have been separated. These regimes are distinguishable as well in the surfaces obtained as in the signals gained by t...

Research paper thumbnail of Simulation, Experimental Investigation and Control of Thermal Behavior in Modular Tool Systems

RADONS:NONLIN.DYN.PROD.SY O-BK, 2004

Research paper thumbnail of Entropy, Complexity, Predictability, and Data Analysis of Time Series and Letter Sequences

The Science of Disasters, 2002

. The structure of time series and letter sequences is investigated using the concepts of entropy... more . The structure of time series and letter sequences is investigated using the concepts of entropy and complexity. First conditional entropy and transinformation are introduced and several generalizations are discussed. Further several measures of complexity are introduced and discussed. ...

Research paper thumbnail of Estimation of parameters and unobserved components for nonlinear systems from noisy time series

Physical review. E, Statistical, nonlinear, and soft matter physics, 2002

We study the problem of simultaneous estimation of parameters and unobserved states from noisy da... more We study the problem of simultaneous estimation of parameters and unobserved states from noisy data of nonlinear time-continuous systems, including the case of additive stochastic forcing. We propose a solution by adapting the recently developed statistical method of unscented Kalman filtering to this problem. Due to its recursive and derivative-free structure, this method minimizes the cost function in a computationally efficient and robust way. It is found that parameters as well as unobserved components can be estimated with high accuracy, including confidence bands, from heavily noise-corrupted data.

Research paper thumbnail of An Approach to a Process Model of Laser Beam Melt Ablation Using Methods of Linear and Nonlinear Data Analysis

RADONS:NONLIN.DYN.PROD.SY O-BK, 2004

Research paper thumbnail of Chaos Theory and Radio Emission

Fragmented Energy Release in Sun and Stars, 1994

ABSTRACT The application of chaos theory has become popular to understand the nature of various f... more ABSTRACT The application of chaos theory has become popular to understand the nature of various features of solar activity because most of them are far from regular. The usual approach, however, that is based on finding low-dimensional structures of the underlying processes seems to be successful only in a few exceptional cases, such as in rather coherent phenomena as coronal pulsations. It is important to note that most phenomena in solar radio emission are more complex. We present two kinds of techniques from nonlinear dynamics which can be useful to analyse such phenomena: Fragmentation processes observed in solar spike events are studied by means of symbolic dynamics methods. Different measures of complexity calculated from such observations reveal that there is some order in this fragmentation. Bursts are a typical transient phenomenon. To study energization processes causing impulsive microwave bursts, the wavelet analysis is applied. It exhibits structural differences of the pre- and post-impulsive phase in cases where the power spectra of both are not distinct.

Research paper thumbnail of Nonlinear Time-Series Analysis of the X-Ray Flux of Compact Objects

Research paper thumbnail of The solar activity cycle is weakly synchronized with the solar inertial motion

Research paper thumbnail of Linear and nonlinear time series analysis of the black hole candidate Cygnus X-1

Research paper thumbnail of CanWe Learn Nonlinear Dynamics from the SS CYG Outburst Series?

Research paper thumbnail of Wavelet Analysis of Solar Flare Hard X‐Rays

The Astrophysical Journal, 1998

THE ASTROPHYSICAL JOURNAL, 505:941 956, 1998 October 1 © 1998. The American Astronomical Society.... more THE ASTROPHYSICAL JOURNAL, 505:941 956, 1998 October 1 © 1998. The American Astronomical Society. All rights reserved. Printed in USA Wavelet Analysis of Solar Flare Hard X-Rays. MARKUS J. ASCHWANDEN 1. ...

Research paper thumbnail of Measures of complexity in signal analysis

AIP Conference Proceedings, 1996

Research paper thumbnail of Reconstruction of grand minima of solar activity from Delta 14 C data - Linear and nonlinear signal analysis

Research paper thumbnail of Reconstruction of grand minima of solar activity from A14C data' Linear and nonlinear signal analysis

Journal of Geophysical Research, 1996

Research paper thumbnail of Non-linear data analysis and statistical techniques in solar radio astronomy

Lecture Notes in Physics, 1995

Research paper thumbnail of Application of Nonlinear Techniques to SS CYG

Research paper thumbnail of The Earth' magnetic field in the last 100 kyr

Rock-magnetic and palaeo-magnetic data from sediments of two Italian lakes provide a reconstructi... more Rock-magnetic and palaeo-magnetic data from sediments of two Italian lakes provide a reconstruction of the Earth' magnetic field in the last 100 kyr. Since the measurements contain also the climate signal, we apply the Independent Component Analysis in order to extract the signal of the Earth' magnetic field.

Research paper thumbnail of Evalutionsbericht des Interdisziplinaren Zentrums fur Dynamik komplexer Systeme (DYKOS)

Research paper thumbnail of On Nonlinear Signal Processing

Research paper thumbnail of Stochastics In Circumplanetary Dust Dynamics

Charged dust grains in circumplanetary environments experience, beyond various de- terministic fo... more Charged dust grains in circumplanetary environments experience, beyond various de- terministic forces, also stochastic perturbations: E.g., fluctuations of the magnetic field, the charge of the grains etc. Here, we investigate the dynamics of a dust population in a circular orbit around the planet which is perturbed by a stochastic magnetic field B , modeled by an isotropi- cally Gaussian white noise. The resulting perturbation equations give rise to a modi- 2 fied diffusion of the inclinations and eccentricities ­ x D [t +/- sin[2nt]/(2n)] (x - alias for eccentricity e and the inclination i, t - time). The diffusion coefficient is found to be D = [G]2/n, where the gyrofrequency and the orbital frequency are denoted by G, and n, respectively. This behavior has been checked by numerical experiments. We have chosen dust grains (1µm in radius) initially moving in circular orbits around a planet (Jupiter) and integrated numerically their trajectories over their typical lifetimes (100 ye...

Research paper thumbnail of Statistical Parameters of a Control Strategy of Laser Beam Melt

Laser beam melt ablation - a contact-free machining process - oers several advantages compared to... more Laser beam melt ablation - a contact-free machining process - oers several advantages compared to conventional processing mechanisms: there exists no tool wear and even extremely hard or brittle materials can be processed. During ablation the workpiece is molten by a CO2-laser beam, this melt is then driven out by the impulse of a process gas. The idea behind laser ablation is rather simple, but it has a major limitation in practical applications: with increasing ablation rates surface quality of the workpiece processed declines rapidly. At high ablation rates, depending on the process parameters dierent periodic-like structures can be observed on the ablated surface. These structures show a dependence on the line energy, which has been identi ed as a fundamental control parameter. In dependence on this parameter several regimes with dierent behaviours of the process have been separated. These regimes are distinguishable as well in the surfaces obtained as in the signals gained by t...

Research paper thumbnail of Simulation, Experimental Investigation and Control of Thermal Behavior in Modular Tool Systems

RADONS:NONLIN.DYN.PROD.SY O-BK, 2004

Research paper thumbnail of Entropy, Complexity, Predictability, and Data Analysis of Time Series and Letter Sequences

The Science of Disasters, 2002

. The structure of time series and letter sequences is investigated using the concepts of entropy... more . The structure of time series and letter sequences is investigated using the concepts of entropy and complexity. First conditional entropy and transinformation are introduced and several generalizations are discussed. Further several measures of complexity are introduced and discussed. ...

Research paper thumbnail of Estimation of parameters and unobserved components for nonlinear systems from noisy time series

Physical review. E, Statistical, nonlinear, and soft matter physics, 2002

We study the problem of simultaneous estimation of parameters and unobserved states from noisy da... more We study the problem of simultaneous estimation of parameters and unobserved states from noisy data of nonlinear time-continuous systems, including the case of additive stochastic forcing. We propose a solution by adapting the recently developed statistical method of unscented Kalman filtering to this problem. Due to its recursive and derivative-free structure, this method minimizes the cost function in a computationally efficient and robust way. It is found that parameters as well as unobserved components can be estimated with high accuracy, including confidence bands, from heavily noise-corrupted data.

Research paper thumbnail of An Approach to a Process Model of Laser Beam Melt Ablation Using Methods of Linear and Nonlinear Data Analysis

RADONS:NONLIN.DYN.PROD.SY O-BK, 2004

Research paper thumbnail of Chaos Theory and Radio Emission

Fragmented Energy Release in Sun and Stars, 1994

ABSTRACT The application of chaos theory has become popular to understand the nature of various f... more ABSTRACT The application of chaos theory has become popular to understand the nature of various features of solar activity because most of them are far from regular. The usual approach, however, that is based on finding low-dimensional structures of the underlying processes seems to be successful only in a few exceptional cases, such as in rather coherent phenomena as coronal pulsations. It is important to note that most phenomena in solar radio emission are more complex. We present two kinds of techniques from nonlinear dynamics which can be useful to analyse such phenomena: Fragmentation processes observed in solar spike events are studied by means of symbolic dynamics methods. Different measures of complexity calculated from such observations reveal that there is some order in this fragmentation. Bursts are a typical transient phenomenon. To study energization processes causing impulsive microwave bursts, the wavelet analysis is applied. It exhibits structural differences of the pre- and post-impulsive phase in cases where the power spectra of both are not distinct.

Research paper thumbnail of Nonlinear Time-Series Analysis of the X-Ray Flux of Compact Objects

Research paper thumbnail of The solar activity cycle is weakly synchronized with the solar inertial motion

Research paper thumbnail of Linear and nonlinear time series analysis of the black hole candidate Cygnus X-1

Research paper thumbnail of CanWe Learn Nonlinear Dynamics from the SS CYG Outburst Series?

Research paper thumbnail of Wavelet Analysis of Solar Flare Hard X‐Rays

The Astrophysical Journal, 1998

THE ASTROPHYSICAL JOURNAL, 505:941 956, 1998 October 1 © 1998. The American Astronomical Society.... more THE ASTROPHYSICAL JOURNAL, 505:941 956, 1998 October 1 © 1998. The American Astronomical Society. All rights reserved. Printed in USA Wavelet Analysis of Solar Flare Hard X-Rays. MARKUS J. ASCHWANDEN 1. ...