Search

Your search keyword '"Kantelhardt, J. W."' showing total 34 results
Start Over Author "Kantelhardt, J. W."
34 results on '"Kantelhardt, J. W."'

2. Evacuation in the Social Force Model is not stationary

Author

Gawroński, P., Kułakowski, K., Kämpf, M., and Kantelhardt, J. W.

Subjects
Physics - Physics and Society
Abstract

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 time lags decrease in time till there are only about 50 pedestrians in the room, then they start to increase. This suggests that at the last stage the flow is laminar. In the first stage, clogging events slow the evacuation down. As they are more likely for larger crowds, the flow is not stationary. The data are investigated with detrended fluctuation analysis., Comment: 7 pages, 3 figures; PACS numbers: 89.75.Fb, 05.40.-a, 05.45.Tp, 89.40.Bb

Published
2011
Full Text
View/download PDF

4. Random walks, fractons, and electrons on percolation structures at criticality

Author

Bunde, A., Dräger, J., Kantelhardt, J. W., Beig, R., editor, Ehlers, J., editor, Frisch, U., editor, Hepp, K., editor, Jaffe, R. L., editor, Kippenhahn, R., editor, Ojima, I., editor, WeidenmÜller, H. A., editor, Wess, J., editor, Zittartz, J., editor, Beiglböck, W., editor, Pękalski, Andrzej, editor, and Sznajd-Weron, Katarzyna, editor

Published
1999
Full Text
View/download PDF

12. Changing climate states and stability: from Pliocene to present

Author

Livina, Valerie, Kwasniok, Frank, Lohmann, Gerrit, Kantelhardt, J. W., Livina, Valerie, Kwasniok, Frank, Lohmann, Gerrit, and Kantelhardt, J. W.

Abstract

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 method on artificial data and then apply it to climate records spanning progressively shorter time periods from 5.3 Myr ago to the recent observational record. We detect various changes in the number and stability of states in the climate system. The onset of Northern Hemisphere glaciation roughly 3 Myr BP is detected as the appearance of a second climate state. During the last ice age in Greenland, there is a bifurcation representing the loss of stability of the warm interstadial state, followed by the total loss of this state around 25 kyr BP. The Holocene is generally characterized by a single stable climate state, especially at large scales. However, in the historical record, at the regional scale, the European monthly temperature anomaly temporarily exhibits a second, highly degenerate (unstable) state during the latter half of the eighteenth century. At the global scale, temperature is currently undergoing a forced movement of a single stable state rather than a bifurcation. The method can be applied to a wide range of geophysical systems with time series of sufficient length and temporal resolution, to look for bifurcations and their precursors.

Published
2011

18. Discrete wavelet approach to multifractality

Author

Kantelhardt, J, Eduardo Roman, H, Greiner, M, Kantelhardt J. W., Eduardo Roman H., Greiner M., Kantelhardt, J, Eduardo Roman, H, Greiner, M, Kantelhardt J. W., Eduardo Roman H., and Greiner M.

Abstract

A new and simple method is presented to study local scaling properties of measures defined on regular and fractal supports. The method, based on a discrete wavelet analysis (WA), complements the well-known multifractal analysis (MA) extensively used in many physical problems. The present wavelet approach is particularly suitable for problems where the multifractal analysis does not provide conclusive results, as e.g. in the case of measures corresponding to Anderson localized wave-functions in one-dimension. Examples of different types of measures are also discussed which illustrate the usefulness of the WA to classify non-multifractal measures according to additional characteristic exponents, which can not be obtained within the MA. © 1995.

Published
1995

21. Random walks, fractons, and electrons on percolation structures at criticality.

Author

Beig, R., Ehlers, J., Frisch, U., Hepp, K., Jaffe, R. L., Kippenhahn, R., Ojima, I., WeidenmÜller, H. A., Wess, J., Zittartz, J., Beiglböck, W., Pękalski, Andrzej, Sznajd-Weron, Katarzyna, Bunde, A., Dräger, J., and Kantelhardt, J. W.

Abstract

We discuss the localization of random walks, vibrational excitations ("fractons"), and electronic wave functions on self similar percolation clusters at criticality. We show that, contrary to the common belief, the localization behavior of random walks differs basically from the behavior of fractons and electrons. This is seen best in the shortest path (chemical) metric: While the distribution of the probability densities at fixed chemical distance l from the origin of the random walk is very narrow (for fixed time t), the distribution of the amplitudes of fractons and electrons at fixed l from their localization center is logarithmically broad (for eigenfunctions with fixed energy E or frequency w). Here we present two different approaches that account for the different localization phenomena considered. The treatments describe satisfactorily the numerical results, in particular the appearance of different localization regimes and the logarithmic dependence of the crossovers on the number of averaged configurations. [ABSTRACT FROM AUTHOR]

Published
1999
Full Text
View/download PDF

33. Correlated and uncorrelated regions in heart-rate fluctuations during sleep.

Author

Bunde A, Havlin S, Kantelhardt JW, Penzel T, Peter JH, and Voigt K

Subjects
Biometry, Humans, Models, Biological, Periodicity, Sleep Apnea Syndromes physiopathology, Sleep, REM physiology, Heart Rate physiology, Sleep Stages physiology
Abstract

Healthy sleep consists of several stages: deep sleep, light sleep, and rapid eye movement (REM) sleep. Here we show that these sleep stages can be characterized and distinguished by correlations of heart rates separated by n beats. Using the detrended fluctuation analysis (DFA) up to fourth order we find that long-range correlations reminiscent to the wake phase are present only in the REM phase. In the non-REM phases, the heart rates are uncorrelated above the typical breathing cycle time, pointing to a random regulation of the heartbeat during non-REM sleep.

Published
2000
Full Text
View/download PDF

34. Heart rate variability during sleep stages in normals and in patients with sleep apnea.

Author

Penzel T, Bunde A, Grote L, Kantelhardt JW, Peter JH, and Voigt K

Subjects
Autonomic Nervous System physiopathology, Humans, Reference Values, Sleep Apnea Syndromes physiopathology, Heart Rate physiology, Polysomnography, Signal Processing, Computer-Assisted, Sleep Apnea Syndromes diagnosis, Sleep Stages physiology
Abstract

Heart rate and heart rate variability are under the control of the autonomous nervous system. It can be assumed that during sleep internal influences dominate the autonomous nervous system. During the different sleep stages heart rate regulation differs in normal subjects. Obstructive sleep apnea is a disorder which has its origin in sleep and has strong modulating effects on the autonomous nervous system with prominent heart rate variations in consequence. In order to separate the influences of sleep stages and sleep apnea on heart rate variability we applied detrended fluctuation analysis in 12 healthy subjects and 20 patients with sleep apnea. We could show that the differences between sleep stages observed in healthy subjects were still present in subjects with sleep apnea despite their cyclical variation in heart rate. We conclude, that detrended fluctuation analysis is able to separate the influences of sleep stages and sleep apnea on heart rate variability.

Published
2000

Catalog

Books, media, physical & digital resources
See catalog results