Jan W Kantelhardt

Martin Luther University Halle-Wittenberg | MLU · Institute of Physics

Some details of cardiovascular and cardio-respiratory regulation and their changes during different sleep stages remain still unknown. In this paper we compared the fluctuations of heart rate, pulse rate, respiration frequency, and pulse transit times as well as EEG alpha-band power on time scales from 6 to 200 s during different sleep stages in or...

We study the localization of tight-binding electrons in loopless random fractal structures modelled by Bethe lattices (Cayley trees) at the percolation threshold. We find the intriguing effect that, for fixed energy, the way the wavefunction decays along the branches of the tree from its center (the so called topological distance) depends on both t...

We study local scaling behavior of amplitude fluctuations of localized Anderson wavefunctions in one and two dimensions. The corresponding measures are analysed by means of the standard multifractal method and by a recently introduced wavelet approach to multifractality. Our calculations suggest that such localized wavefunctions are not mutlifracta...

We systematically compare strengths and weaknesses of two methods that can be used to quantify causal links between time series: Granger-causality and Bivariate Phase Rectified Signal Averaging (BPRSA). While a statistical test method for Granger-causality has already been established, we show that BPRSA causality can also be probed with existing s...

Propofol sedation during endoscopic interventions is a well-established and generally safe procedure. However, the risk for adverse events increases considerably in long interventions, emergencies and patients with certain comorbidities. To this day, there is no objective device to monitor sedation depth. Brain monitors have been developed for gene...

Freezing of gait (FoG), a paroxysmal gait disturbance commonly experienced by patients with Parkinson’s disease (PD), is characterized by sudden episodes of inability to generate effective forward stepping. Recent studies have shown an increase in beta frequency of local-field potentials in the basal-ganglia during FoG, however, comprehensive resea...

Objective: Nocturnal recordings of heart rate and respiratory rate usually require several separate sensors or electrodes attached to different body parts -- a disadvantage for at-home screening tests and for large cohort studies. In this paper, we demonstrate that a state-of-the-art accelerometer placed at subjects' wrists can be used to derive r...

The forest fire model in statistical physics represents a paradigm for systems close to but not completely at criticality. For large tree growth probabilities p we identify periodic attractors, where the tree density ρ oscillates between discrete values. For lower p this self-organized multistability persists with incrementing numbers of states. Ev...

Propofol sedation during endoscopic interventions is a well-established and generally safe procedure. However, the risk for adverse events increases considerably in long interventions, emergencies and patients with certain comorbidities. To this day, there is no objective device to monitor sedation depth. Brain monitors have been developed for gene...

Background: Reliable and safe sedation is a prerequisite for endoscopic interventions. The current standard is rather safe, yet, an objective device to measure sedation depth is missing. To date, anaesthesia monitors based on processed electroencephalogram (EEG) have not been utilised in conscious sedation. Objective: To investigate EEG paramete...

Respiratory rate and changes in respiratory activity provide important markers of health and fitness. Assessing the breathing signal without direct respiratory sensors can be very helpful in large cohort studies and for screening purposes. In this paper, we demonstrate that long-term nocturnal acceleration measurements from the wrist yield signific...

The high temporal and intensity resolution of modern accelerometers gives the opportunity of detecting even tiny body movements via motion-based sensors. In this paper, we demonstrate and evaluate an approach to identify pulse waves and heartbeats from acceleration data of the human wrist during sleep. Specifically, we have recorded simultaneously...

In this paper, we apply novel techniques for characterizing leg muscle activation patterns via electromyograms (EMGs) and for relating them to changes in electroencephalogram (EEG) activity during gait experiments. Specifically, we investigate changes of leg-muscle EMG amplitudes and EMG frequencies during walking, intentional stops, and unintended...

In obstructive sleep apnea, patients’ sleep is fragmented leading to excessive daytime sleepiness and co‐morbidities like arterial hypertension. However, traditional metrics are not always directly correlated with daytime sleepiness, and the association between traditional sleep quality metrics like sleep duration and arterial hypertension is still...

We propose a biased diffusion model of accumulated subthreshold voltage fluctuations in wake-promoting neurons to account for stochasticity in sleep dynamics and to explain the occurrence of brief arousals during sleep. Utilizing this model, we derive four neurophysiological parameters related to neuronal noise level, excitability threshold, deep-s...

Introduction: Parkinson's disease (PD) is characterized by gait disturbances, which become severe during the advanced stages of the disease. Though gait impairments in Parkinson's disease have been extensively described in terms of spatiotemporal gait parameters, little is known regarding associated patterns of cortical activity. The objective of...

We studied whether interhemispheric synchronization (Inter-PS), as reflected by EEG signals, is altered in Parkinson’s disease (PD) during walking, and analyze its potential implications for freezing of gait (FOG).

The appreciation for the need to record electroencephalographic (EEG) signals from humans while walking has been steadily growing in recent years, particularly in relation to understanding gait disturbances. Movement artefacts (MA) in EEG signals originate from mechanical forces applied to the scalp electrodes, inducing small electrode movements re...

Introduction Large field studies now check for the prevalence of sleep apnea using simplified low cost recording technologies. A national field study on 200.000 persons investigates a subset of 40.000 persons with actigraphy and single-lead 24-hour ECG to check for arrhythmias and sleep apnea. Methods In order to validate the actigraphy and 24-hou...

Background Sleep can be conceptualized as a sequence of discernable vigilance states (sleep stages). When the polysomnogram is decomposed into bouts of subsequent epochs of the same sleep stage it can be shown from sufficiently large data bases that bout lengths follow a stochastic process characterized e.g. by exponential of power law distribution...

Recently, time delay stability analysis of biosignals has been successfully applied as a multivariate time series analysis method to assess the human physiological network in young adults. The degree of connectivity between different network nodes is described by the so-called link strength. Based on polysomnographic recordings (PSGs), it could be...

Objective: Phase synchronization between two weakly coupled oscillators occurs in many natural systems. Since it is difficult to unambiguously detect such synchronization in experimental data, several methods have been proposed for this purpose. Five popular approaches are systematically optimized and compared here. Approach: We study and apply...

Accelerometry can be a practical replacement for polysomnography in large observational studies. This review discusses the need for sleep characterization in large observational studies, exemplified by the practices of the ongoing German National Cohort study. After brief descriptions of the physical principles and state-of-the-art accelerometer de...

Study objectives: We investigate how characteristics of sleep-wake dynamics in humans are modified by narcolepsy, a clinical condition that is supposed to destabilize sleep-wake regulation. Subjects with and without cataplexy are considered separately. Differences in sleep scoring habits as a possible confounder have been examined. Methods: Four...

The cardiac component of cardio-respiratory polysomnography is covered by ECG and heart rate recordings. However, their evaluation is often underrepresented in summarizing reports. As complements to EEG, EOG, and EMG, these signals provide diagnostic information for autonomic nervous activity during sleep. This review presents major methodological...

Can online media predict new and emerging trends, since there is a relationship between trends in society and their representation in online systems? While several recent studies have used Google Trends as the leading online information source to answer corresponding research questions, we focus on the online encyclopedia Wikipedia often used for d...

We study short-term and long-term persistence properties (related with auto-correlations) of amplitudes and frequencies of EEG oscillations in 176 healthy subjects and 40 patients during nocturnal sleep. The amplitudes show scaling from 2 to 500 seconds (depending on the considered band) with large fluctuation exponents during (nocturnal) wakefulne...

The recording of ECG and heart rate are indispensable parameters of cardiorespiratory polysomnography. Complementing neurophysiological signals this allows an assessment of the autonomous nervous regulation during sleep. An evaluation of the nocturnal ECG is possible in terms of cyclical variations of heart rate and in terms of respiration modulate...

Can online media predict new and emerging trends? The underlying assumption is that a direct relationship exists between trends in emerging technological and social trends and their representation in online systems. While several recent studies have focused on Google as the leading online information source to answer this question, much less attent...

The aim was to evaluate the inter-rater reliability in scoring sleep stages in two sleep labs in Berlin Germany and Beijing China. The subjects consist of polysomnography (PSGs) from 15 subjects in a German sleep laboratory, with 7 mild to moderate sleep apnea hypopnea syndrome (SAHS) patients and 8 healthy controls, and PSGs from 15 narcolepsy pat...

Since the numbers of hypertext pages and hyperlinks in the WWW have been continuously growing for more than 20 years, the problem of finding relevant content has become increasingly important. We have developed and evaluated techniques for a time-dependent characteri-zation of the global and local relevance of WWW pages based on document length, nu...

While many microscopic models of traffic flow describe transitions between different traffic phases, such transitions are difficult to quantify in measured traffic data. Here we study long-term traffic recordings consisting of ≈2900 days of flow, density, and velocity time series with minute resolution from a Spanish motorway. We calculate fluctuat...

We study the effective scaling behavior of high-resolution accelerometric time series recorded at the wrists and hips of 100 subjects during sleep and wake. Using spectral analysis and detrended fluctuation analysis we find long-term correlated fluctuations with a spectral exponent beta approximate to 1.0 (1/f noise). On short time scales, beta is...

This report summarizes the results of a short-term student research project focused on the usage of Swedish Wikipedia. It is trying to answer the following question: To what extent (and why) do people from non-English language communities use the English Wikipedia instead of the one in their local language? Article access time series and article ed...

The paper describes a computational framework for time-series analysis. It allows rapid prototyping of new algorithms, since all components are re-usable. Generic data structures represent different types of time series, e. g. event and interevent time series, and define reliable interfaces to existing big data. Standalone applications, highly scal...

In an emergency situation, imitation of strategies of neighbours can lead to an order-disorder phase transition, where spatial clusters of pedestrians adopt the same strategy. We assume that there are two strategies, cooperating and competitive, which correspond to a smaller or larger desired velocity. The results of our simulations within the Soci...

Internet-based social networks often reflect extreme events in nature and society by drastic increases in user activity. We study and compare the dynamics of the two major complex processes necessary for information spread via the online encyclopedia ‘Wikipedia’, i.e., article editing (information upload) and article access (information viewing) ba...

Network theory has become one of the most visible theoretical frameworks that can be applied to the description, analysis, understanding, design and repair of multi-level complex systems. Complex networks occur everywhere, in man-made and human social systems, in organic and inorganic matter, from nano to macro scales, and in natural and anthropoge...

Integrated physiological systems, such as the cardiac and the respiratory system, exhibit complex dynamics that are further influenced by intrinsic feedback mechanisms controlling their interaction. To probe how the cardiac and the respiratory system adjust their rhythms, despite continuous fluctuations in their dynamics, we study the phase synchro...

The human organism is an integrated network where complex physiological systems, each with its own regulatory mechanisms, continuously interact, and where failure of one system can trigger a breakdown of the entire network. Identifying and quantifying dynamical networks of diverse systems with different types of interactions is a challenge. Here we...

The human organism is an integrated network where complex physiologic systems, each with its own regulatory mechanisms, continuously interact, and where failure of one system can trigger a breakdown of the entire network. Identifying and quantifying dynamical networks of diverse systems with different types of interactions is a challenge. Here, we...

Internet-based social networks (as novel information and communication platforms) often reflect the dynamics of changing interests and activities in society by characteristic usage patterns. Here we study the dynamics of user access-rate time series and edit-interval time series for all articles in the online encyclopedia “Wikipedia” with access ra...

We present a recently developed method of potential analysis of time series data, which comprises (1) derivation of the number of distinct global states of a system from time series data, and (2) derivation of the potential coefficients describing the location and stability of these states, using the unscented Kalman filter (UKF). We test the metho...

We studied and compared the autocorrelation behaviour and the temporal multifractal properties of long daily river discharge and precipitation records from 42 hydrological stations and 99 meteorological stations around the globe. To determine the scaling behaviour in the presence of trends , we applied detrended fluctuation analysis (DFA) and multi...

We study the performance of multifractal detrended fluctuation analysis (MF-DFA) applied to long-term correlated and multifractal data records in the presence of additive white noise, short-term memory and periodicities. Such additions and disturbances that can be typically found in the observational records of various complex systems ranging from...

We address two common major problems in the study of time series characterizing fluctuations in complex systems: multifractal analysis and multifractal modeling. Specifically, we introduce a multi-fractal centered moving average (MF-CMA) analysis, which is computationally easier but equivalently performing compared with the well-established multi-f...

In this chapter we consider the role played by Anderson localization in transport through complex networks, for example, an optical network. The network is described by a tight binding Hamiltonian, which may be used to determine the properties of the Anderson transition according to the statistical properties of its eigenvalues. The Anderson transi...

An evacuation process is simulated within the Social Force Model. Thousand pedestrians are leaving a room by one exit. We investigate the stationarity of the distribution of time lags between instants when two successive pedestrians cross the exit. The exponential tail of the distribution is shown to gradually vanish. Taking fluctuations apart, the...

We review our studies of the statistics of return intervals and extreme events (block maxima) in long-term correlated data sets, characterized by a power-law decaying autocorrelation function with correlation exponent γ between 0 and 1, for different distributions (Gaussian, exponential, power-law, and log-normal). For the return intervals, the lon...

Fruhere Studien haben gezeigt, dass die Variabilitat der Atmung und der Herzfrequenz ein fraktales Skalierungsverhalten aufweisen. In dieser Untersuchung haben wir nun die Kurzzeit und die Langzeit Korrelationen der Herzfrequenz und der Atmungsfrequenz Daten bei Probanden ohne Schlafstorungen untersucht und hierbei speziell die Alterabhangigkeit be...

Sleep is an active and regulated process with restorative functions for physical and mental conditions. Based on recordings of brain waves and the analysis of characteristic patterns and waveforms it is possible to distinguish wakefulness and five sleep stages. Sleep and the sleep stages modulate autonomous nervous system functions such as body tem...

Respiratory and heart rate variability exhibit fractal scaling behavior on certain time scales. We studied the short-term and long-term correlation properties of heartbeat and breathing-interval data from disease-free subjects focusing on the age-dependent fractal organization. We also studied differences across sleep stages and night-time wake and...

We apply a new method of potential analysis to study several paleo and historic climatic records. The method comprises (i) derivation of the number of distinct global states of a system from time series, (ii)derivation of the potential coefficients using an Unscented Kalman Filter (UKF), yielding indications of possible bifurcations and transitions...

IntroductionComplex NetworksModels with Localization–Delocalization TransitionsLevel StatisticsLocalization–Delocalization Transitions in Complex NetworksConclusion References

We study the effects of Parkinson's disease (PD) on phase synchronisation and cross-modulation of instantaneous amplitudes and frequencies for brain waves during sleep. Analysing data from 40 full-night EEGs (electro-encephalograms) of ten patients with PD and ten age-matched healthy controls we find that phase synchronisation between the left and...

We present an example of the use of analytical models to predict global properties of large-scale information technology systems from the parameters of simple local interactions. The example is intended as a first step towards using complex systems modeling methods to control self-organization in organic systems. It is motivated by a concrete appli...

We study precipitation patterns occurring in diffusion-limited reactions, focusing on Liesegang bands. Naturally, these patterns are non-equidistantly spaced, and thus less useful for bottom-up material design. However, we show how a continuous large-scale modification of the inhomogeneity of the substrate and/or the nucleation threshold can be use...

We study the effects of Parkinson's disease (PD) on phase synchronisation and cross-modulation of instantaneous amplitudes and frequencies for brain waves during sleep. Analysing data from 40 full-night EEGs (electro-encephalograms) of ten patients with PD and ten age-matched healthy controls we find that phase synchronisation between the left and...

Changes in the phase-synchronization behavior of a physiological system can characterize the complexity of its dynamics. Taking the human cardio-respiratory system as an example and using a recently developed procedure for an auto-mated screening of synchrograms we study the data of 874 post-infarction patients, where heartbeat intervals and respir...

Heartbeat interval fluctuations exhibit fractal scaling behavior on certain time scales. However, less is known about blood pressure fluctuations and respiration. We compare the short-term and long-term scaling properties of heartbeat intervals (HBI), systolic (SBP) and diastolic (DBP) blood pressure as well as respiratory (RES) time series based o...

Results of modulation analysis of instantaneous amplitudes (a) and frequencies (d) as well as amplitude-frequency cross-modulation analysis (b,c) during periods of wakefulness. The four 36 x 36 matrices show the modulation coefficients γ + [(c) and upper triangles in (a,d)] and γ − [(b) and lower triangles in (a,d)] with modulation degrees increasi...