Biomedical subjects

M Schiek

Publications and source records attributed to M Schiek.

5 recordsLinked to original sources

PubMed2006

Water adsorption on the hydroxylated H-(1x1) O-ZnO(0001) surface.

The adsorption of water multilayers on a well defined single crystal, hydroxyl-terminated ZnO-surface, H(1x1)-O-ZnO(0001) surface has been investigated using infrared (IR) spectroscopy, helium atom scattering (HAS) and X-ray photoelectron spectroscopy (XPS). The results reveal the formation of well ordered mono-, bi- and multilayers of D2O and H2O on this substrate. On the bare hydroxyl-covered H(1x1) surface the OH-stretch vibration could be clearly identified in the IR-spectra. The water adsorption and desorption kinetics on this hydroxylated surface were studied by monitoring the reflectivity of the surface for helium atoms. The analysis of the data yielded activation energies for desorption of H2O from the H(1x1) O-ZnO surface of 55.2 kJ mol-1. The results reveal the formation of ordered mono- and bilayers. Further exposure to water at 113 K results in the formation of amorphous 3-D islands.

Journal Article↗

PubMed2006

Nanofiber frequency doublers.

Nanoscaled, needle-shaped frequency doublers have been generated via self-assembled surface growth from functionalized quaterphenylene molecules with a designed large hyperpolarizability. The nanofiber frequency doublers exhibit very weak fluorescence centered around 430 nm but emit a strong, resonance-enhanced second-harmonic signal when excited with infrared 80 fs laser pulses. The frequency doublers are employed to correlate second-harmonic response and morphology via two-dimensional true second-harmonic images of individual nanoaggregates obtained with the help of a femtosecond laser scanning microscope.

Journal Article↗

PubMed1998

One-dimensional, nonlinear determinism characterizes heart rate pattern during paced respiration.

This study focuses on the dynamic pattern of heart rate variability in the frequency range of respiration, the so-called respiratory sinus arrhythmia. Forty experimental time series of heart rate data from four healthy adult volunteers undergoing a paced respiration protocol were used as an empirical basis. For pacing-cycle lengths >8 s, the heartbeat intervals are shown to obey a rule that can be expressed by a one-dimensional circle map (next-angle map). Circle maps are introduced as a new type of model for time series analyses to characterize the nonlinear dynamic pattern underlying the respiratory sinus arrhythmia during voluntary paced respiration. Although these maps are not chaotic, the dynamic pattern shows typical imprints of nonlinearity. By starting from a piecewise linear model, which describes the different circle maps obtained from the empirical time series for various pacing frequencies, time invariant measures can be introduced that characterize the dynamic pattern of heart rate variability during voluntary slow-paced respiration.

Adult↗

PubMed1995

[Methodology in the analysis of asymmetry in fluctuations of heart rate].

Time series of R-R intervals show fluctuations which are neither symmetric regarding the changes in length of heart beats nor regarding the number of heart beats during the phases of heart rate acceleration and deceleration. These features of heart rate variability cannot be quantified by the analysis of the beat-to-beat variability or by the spectrum analysis of heart rate. The analysis of asymmetry using the distribution function of the differences between consecutive R-R intervals creates measures for the total, central, and peripheral asymmetry. These measures quantify different aspects of the shape of the distribution function. The asymmetry measures are either based on the amount of difference between consecutive R-R intervals or the number of lengthening R-R intervals in a sequence of heart beats. The analysis of asymmetry of R-R interval time series shows differences among test subjects during rest.

Circadian Rhythm↗

PubMed1995

[Mathematical model of "respiratory sinus arrhythmia"].

We developed a mathematical model of "respiratory" sinus arrhythmia. The model combines a representation continuous in time of the parasympathetic and sympathetic innervation and the membrane potential of the pace maker cell of the heart with a beat-by-beat representation of the cardiovascular variables like diastolic and systolic blood pressure, pulse pressure, total peripheral resistance and baroreceptor activity. The influence of respiration is described separately by mechanical and central neural mechanisms. Using this nonlinear model of "respiratory" heart rate variability one is able to explore in a theoretical way the different heart rate variability generating mechanisms, either as isolated or combined effects on both, heart rate variability in the frequency range of respiration and in the frequency range around 0.1 Hz. By fitting a simulated RR interval time course to a physiological RR interval time course one can estimate the relative weight of the different mechanisms generating this physiological heart rate variability.

Arrhythmia, Sinus↗