TY - JOUR A1 - Wessel, Niels A1 - Voss, Andreas A1 - Malberg, Hagen A1 - Ziehmann, Christine A1 - Voss, Henning U. A1 - Schirdewan, Alexander A1 - Meyerfeldt, Udo A1 - Kurths, Jürgen T1 - Nonlinear analysis of complex phenomena in cardiological data N2 - The main intention of this contribution is to discuss different nonlinear approaches to heart rate and blood pressure variability analysis for a better understanding of the cardiovascular regulation. We investigate measures of complexity which are based on symbolic dynamics, renormalised entropy and the finite time growth rates. The dual sequence method to estimate the baroreflex sensitivity and the maximal correlation method to estimate the nonlinear coupling between time series are employed for analysing bivariate data. The latter appears to be a suitable method to estimate the strength of the nonlinear coupling and the coupling direction. Heart rate and blood pressure data from clinical pilot studies and from very large clinical studies are analysed. We demonstrate that parameters from nonlinear dynamics are useful for risk stratification after myocardial infarction, for the prediction of life-threatening cardiac events even in short time series, and for modelling the relationship between heart rate and blood pressure regulation. These findings could be of importance for clinical diagnostics, in algorithms for risk stratification, and for therapeutic and preventive tools of next generation implantable cardioverter defibrillators. Y1 - 2000 ER - TY - JOUR A1 - Voss, Henning U. A1 - Timmer, Jens A1 - Kurths, Jürgen T1 - Modeling and identification of nonlinear systems Y1 - 2004 SN - 0218-1274 ER - TY - JOUR A1 - Voss, Henning U. A1 - Timmer, Jens A1 - Kurths, Jürgen T1 - Nonlinear dynamical system identification from uncertain and indirect measurements N2 - We review the problem of estimating parameters and unobserved trajectory components from noisy time series measurements of continuous nonlinear dynamical systems. It is first shown that in parameter estimation techniques that do not take the measurement errors explicitly into account, like regression approaches, noisy measurements can produce inaccurate parameter estimates. Another problem is that for chaotic systems the cost functions that have to be minimized to estimate states and parameters are so complex that common optimization routines may fail. We show that the inclusion of information about the time-continuous nature of the underlying trajectories can improve parameter estimation considerably. Two approaches, which take into account both the errors-in-variables problem and the problem of complex cost functions, are described in detail: shooting approaches and recursive estimation techniques. Both are demonstrated on numerical examples Y1 - 2004 SN - 0218-1274 ER - TY - JOUR A1 - Sitz, Andre A1 - Schwarz, Udo A1 - Kurths, Jürgen A1 - Voss, Henning U. T1 - Estimation of parameters and unobserved components for nonlinear systems from noisy time series N2 - 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. Y1 - 2002 UR - http://pre.aps.org/ ER - TY - INPR A1 - Voss, Henning A1 - Kurths, Jürgen A1 - Schwarz, Udo T1 - Reconstruction of grand minima of solar activity from Delta 14 C data : linear and nonlinear signal analysis N2 - Using a special technique of data analysis, we have found out 34 grand minima of solar activity obtained from a 7,700 years long Δ14C record. The method used rests on a proper filtering of the Δ14C record and the extrapolation of verifiable results for the later history back in time. Additionally, we use a method of nonlinear dynamics, the recurrence rate, to back up the results. Our findings are not contradictory to the record of solar maxima resp. minima by Eddy [5], but constitute a considerable extension. Hence, it has become possible to look closer at the validity of models. This way, we have tested several models for solar activity, esp. the model of Barnes et al. [1]. There are hints for that the grand minima might solely be driven by the 209 year period found in the Δ14C record. T3 - NLD Preprints - 28 Y1 - 1996 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-14083 ER - TY - JOUR A1 - Voss, Henning U. A1 - Kurths, Jürgen A1 - Schwarz, Udo T1 - Reconstruction of grand minima of solar activity from radiocarbon data : linear and nonlinear signal analysis N2 - Using a special technique of data analysis, we have found out 34 grand minima of solar activity in a 7,700 years long C14 record. The method used rests on a proper filtering of the C14 record and the extrapolation of verifiable results for the later history back in time. Additionally, we have applied a method of nonlinear dynamics, the recurrence rate, to back up the results. Our findings are not contradictory to the record of grand minima by Eddy, but constitute a considerable extension. Hence, it has become possible to look closer at the validity of models. This way, we have tested esp. the model of Barnes et al. There are hints for that the grand minima might solely be driven by the 209--year period found in the C14 record. Y1 - 1996 UR - http://www.agnld.uni-potsdam.de/~shw/Paper/vks.ps.gz ER - TY - JOUR A1 - Voss, Henning U. A1 - Bünner, M. J. A1 - Abel, Markus T1 - Identification of continuous, spatiotemporal systems Y1 - 1998 UR - http://www.stat.physik.uni-potsdam.de/~markus/papers/PRE57-2820.pdf ER - TY - THES A1 - Voss, Henning U. T1 - Nichtlineare statistische Methoden zur Datenanalyse Y1 - 1998 ER - TY - JOUR A1 - Voss, Henning U. A1 - Kurths, Jürgen T1 - Test for nonlinear dynamical behavior in symbol sequences Y1 - 1998 ER - TY - JOUR A1 - Voss, Henning U. A1 - Kurths, Jürgen T1 - Reconstruction of nonlinear time delay models from data by the use of optimal transformations Y1 - 1997 ER - TY - BOOK A1 - Voss, Henning U. A1 - Kurths, Jürgen A1 - Schwarz, Udo T1 - Reconstruction of grand minima of solar activity from radiocarbon data : linear and nonlinear signal analysis T3 - Preprint NLD Y1 - 1996 VL - 28 PB - Univ. CY - Potsdam ER - TY - JOUR A1 - Feudel, Ulrike A1 - Jansen, Wolfgang A1 - Kurths, Jürgen A1 - Schwarz, Udo A1 - Voss, Henning U. T1 - Solar variability : simple models and proxy data Y1 - 1997 SN - 4-274-90187-4 ER - TY - JOUR A1 - Timmer, Jens A1 - Schwarz, Udo A1 - Voss, Henning U. A1 - Wardinski, Ingo A1 - Belloni, Tomaso A1 - Hasinger, Günther A1 - VanDerKlis, Michael A1 - Kurths, Jürgen T1 - Linear and Nonlinear Time Series Analysis of the Black Hole Candidate Cygnus X-1 N2 - We analyze the variability in the x-ray lightcurves of the black hole candidate Cygnus X-1 by linear and nonlinear time series analysis methods. While a linear model describes the overall second order properties of the observed data well, surrogate data analysis reveals a significant deviation from linearity. We discuss the relation between shot noise models usually applied to analyze these data and linear stochastic autoregressive models. We debate statistical and interpretational issues of surrogate data testing for the present context. Finally, we suggest a combination of tools from linear and nonlinear time series analysis methods as a procedure to test the predictions of astrophysical models on observed data. Y1 - 2000 UR - http://pre.aps.org/ ER - TY - JOUR A1 - Voss, Henning U. A1 - Kurths, Jürgen T1 - Reconstruction of nonlinear time-delayed feedback models from optical data Y1 - 1999 ER - TY - THES A1 - Voss, Henning U. T1 - Nichtlineare statistische Methoden zur Datenanalyse T2 - Stoffdynamik in Geosystemen Y1 - 1999 SN - 0949-4731 VL - 3 PB - Selbstverl. der Arbeitsgruppe Stoffdynamik in Geosystemen CY - Potsdam ER - TY - JOUR A1 - Kolodner, P. A1 - Abel, Markus A1 - Kurths, Jürgen A1 - Voss, Henning U. T1 - Amplitude equations from spatiotemporal binary-fluid convection data Y1 - 1999 UR - http://www.stat.physik.uni-potsdam.de/~markus/papers/PRL83-3422.pdf ER - TY - JOUR A1 - Schwache, A. A1 - Kurths, Jürgen A1 - Mitschke, F. A1 - Voss, Henning U. T1 - Equations of motion from chaotic data : a driven optical fiber ring resonator Y1 - 1999 ER - TY - JOUR A1 - Voss, Henning A1 - Meyer, Jeannette A1 - Schwonbeck, Susanne A1 - Fritsche, Immo A1 - Hartmann, Bernhard A1 - Wegwarth, Odette A1 - Friedrich, Anke A1 - Buchheister-Knappe, Stefanie A1 - Marwan, Norbert A1 - Bandau, Anja A1 - Bullinger, Hans-Jörg A1 - Weith, Thomas T1 - Portal alumni T2 - Das Ehemaligen-Magazin der Universität Potsdam N2 - Liebe Leserin, lieber Leser, erforschen, was die Welt im Innersten zusammenhält- das ist für viele Studierende ein Traum. Doch welche Opfer muss man bringen, um ihn zu verwirklichen? Welche Bemfsperspektive hat der Bemf Forscher heute noch? Auch viele Absolventen der Universität Potsdam müssen sich diese Fragen beantworten. Zu welchen Antworten einige dabei gekommen sind und welche Probleme sie zu bewältigen haben, vom Spaß am Forschen und von Zukunftsängsten berichten sie in der Rubrik "Forscherkarrieren". Gelder für die Forschung fließen in Deutschland zu spärlich, verglichen mit anderen führenden Industrienationen. So sind die Bedingungen für Forscher hierzulande nicht die besten. Manchen jungen Wissenschaftler zieht es- mitunter notgedrungen- ins Ausland. Wie Deutschland dadurch seine ZukunftsHihigkeit riskiert, thematisiert der Präsident der Fraunhofer-Gesellschaft, Prof. Dr. Hans-Jörg Bullinger, in der Rubrik "wissenstransfer". Auch die Universität ist kein Garant für eine gesicherte Zukunft in der Forschung. Wer sechs Jahre nach der Promotion den Sprung zur Professur nicht geschafft hat, geht einer ungewissen Zukunft als Privatdozent entgegen. Seit einigen Jahren gibt es neben der Habilitation noch einen zweiten Weg zur Professur- die Juniorprofessur. Auch an der Universität Potsdam gibt es seit 2002 Juniorprofessoren, von denen die ersten jetzt evaluiert wurden. Näheres dazu finden Sie ebenfalls in der Rubrik "wissenstransfer". Wer noch nach einer Finanzierungsmöglichkeit für seine Promotion sucht, findet Tipps in der Rubrik "wegweiser". Die Redaktion wünscht Ihnen viel Vergnügen beim Lesen von Portal alumni und freut sich auf zahlreiche Leserbriefe. N2 - Dear readers, many students dream of researching the world's inner and outermost secrets. Still, what sacrifice must one bring in order to achieve this goa/, and what are the professional perspectives being offered to researchers today? Many University of Potsdom alumni have to find answers to these questions as weil. in the section "forscher/eben", a number of alumni discuss their answers, the problems that they have encountered along the way, the enJoyment that they have received through their research and their worries for the future. In Germany, the funding of research on part ofboth the state and the corporate world is sparsein comparison to other leading industrial countries, and the current opportunities for researchers are clearly not the best. in the section ,.wissenstransfer", the president of the Frauenhofer-Gesellschaft, Prof Dr. Hans-jörg Bullinger, discusses how Germany is losing its future potential in the process. Indeed, the university is no guarantee for a secure profossianal future in the research field. A few years ago, the Junior professorship was created as a second path to a Juli professorship, next to the traditional postdoctoral qualification (Habilitation). in 2002, the University of Potsdom began to establish Junior professorships. The first of these are currently being evaluated. More information on this process can be found in the section "wissenstransfer". In addition, suggestions and tips can be found in the section "wegweiser" for those who are seekingfunding opportunities for their dissertation work. T3 - Portal alumni : das Ehemaligen-Magazin der Universität Potsdam - 3/2005 Y1 - 2005 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-481608 VL - 2005 IS - 3 EP - 58 ER -