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K Bräuer

Publications and source records attributed to K Bräuer.

8 recordsLinked to original sources
PubMed2001

Master-slave synchronization in chaotic discrete-time oscillators.

In this paper, we study a simple discrete-time neural oscillator model that, in certain parameter regimes, exhibits periodic or chaotic dynamics. The present model with intrinsically chaotic dynamics is capable of spatiotemporal information processing: in response to constant external stimulation, the oscillator can switch into different chaotic states restricted to distinct parts of the phase space. Of particular interest is the processing of time-dependent input in a master-slave configuration of two coupled oscillators. Here, the response of an oscillator is studied by driving it with the signal of the other. Following the input, the response system adapts to the state of the drive. For a chaotic drive, we can observe generalized synchronization. The onset of adaptation to the drive state by the response is accompanied by on-off intermittency resulting in irregular bursting behavior.

Journal Article↗
PubMed1999

A small-size neural network for computing with strange attractors.

A small-size model for a chaotic neural network is proposed using strange attractors for computation. This network has a chaotic ground state and is capable of responding to external stimuli by constraining the network dynamics to specific parts of the ground state attractor. For parameter optimization, bifurcation diagrams are evaluated.

Journal Article↗
PubMed1999

Nonlinear analysis of blood flux in human vessels.

Laser Doppler fluxmetry (LDF) is frequently used in research on microcirculation of blood. Usually LDF time series are analysed by conventional linear methods, mainly Fourier analysis. These methods may not be optimal for the investigation of nonlinear effects of vasomotion, heartbeat or vessels. Nonlinear methods are based on a reconstruction of the system trajectory in an embedding space describing not only the measured time series but the behaviour of the whole system. The fill factor is a tool for displaying the main properties of this attractor in two dimensions and for determining diverse parameters for further analysis. A quantitative characterization of the system is possible by the distribution of correlation dimensions in the embedding space. The singular value decomposition (SVD) can be used to display and characterize individual degrees of freedom. These methods were applied to LDF time series from nine healthy controls and nine patients with Raynaud's phenomenon due to connective tissue disease. The fill factor and the SVD indicate qualitatively that in the controls vasomotion and heartbeat are the main influences on blood flow and act fairly independently of each other. In the patients there was a mixture of strong but irregular degrees of freedom. The mean and the maximal local correlation dimensions were significantly higher in the patient group. Nonlinear analysis of LDF time series provides additional information which cannot be detected using conventional approaches.

Adult↗
PubMed1998

Skin thermoregulation during local cooling in healthy volunteers and patients with systemic sclerosis--synchronous assessment of capillary red blood cell velocity, laser Doppler flux and skin temperature.

BACKGROUND: Patients with Raynaud's phenomenon due to systemic sclerosis exhibit a functional microangiopathy with endothelial cell damage. The aim of this study was to assess differences in the so-called nutritive and thermoregulative skin blood flow and to obtain further information by Fourier transformation and by nonlinear analysis of laser Doppler flux (LDF) time series. PATIENTS AND METHODS: A local cold stress test was performed in 10 patients and 10 age- and sex-matched healthy controls. Significant differences were detected between nutritive blood flow in the nailfold capillaries, assessed by capillary red blood cell velocity (CBV), and thermoregulatory blood flow, which was synchronously assessed by LDF. RESULTS: CBV was reduced during cooling, the drop being significantly larger in the patients than in the controls. In contrast, there was no significant difference in the decrease of LDF during cooling. The difference between the fall in CBV values and that in LDF was significantly more pronounced in patients. Further analysis of the LDF frequency spectrum by fast Fourier transformation revealed a significantly greater decrease in amplitude at the heart frequency level in healthy volunteers. A further analysis of the LDF signal revealed significant differences at rest and after cooling in fractal dimensions, suggesting an increased complexity of LDF signals in patients. SUMMARY: The patient's increased sensitivity towards local cold cn be observed best at the capillary level. But the changes of LDF in the frequency spectrum during cooling as calculated by fast Fourier transformation revealed significant differences. In addition differences in fractal dimensions of LDF time series suggest that an analysis of nonlinear dynamics may be a promising approach.

Adult↗
PubMed1976

[Evaluation of orthodontic cases by means of key-punch cards. 3. Data from follow-up examinations].

484 orthodontic patients were subjected to follow-up examination. The kind of treatment, the evaluation and the factors that are of importance to continuing successes and recurrences, respectively, are described. It is pointed out that the present communication and the two previous ones aim at illustrating that the orthodontic practitioner is able to document and evaluate his cases easily with the aid of key-word cards.

Activator Appliances↗
PubMed1975

[Interpretation of orthodontically treated by means of punched cards. 2. Data at the completion of treatment].

The authors analysed the key-word cards of 3245 terminated orthodontic cases. Statistical data were obtained about treatment results, therapeutical aids, duration of treatment and co-operation of the patients. These data give a survey on the achievements of the orthodontic practitioner, the choice of his methods and the utilization of his therapeutical aids. The authors could draw certain conclusions as to their own work in practice. Furthermore, they realized that the use of key-word cards permits to evaluate critically their achievements and to perform collective scientific studies.

Dental Records↗