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Biomedical subjects

G Morfill

Publications and source records attributed to G Morfill.

24 records · Page 2Linked to original sources
PubMed2000

NonliNEAR vertical oscillations of a particle in a sheath of a rf discharge.

A new simple method to measure the spatial distribution of the electric field in the plasma sheath is proposed. The method is based on the experimental investigation of vertical oscillations of a single particle in the sheath of a low-pressure radio-frequency discharge. It is shown that the oscillations become strongly nonlinear as the amplitude increases. The theory of anharmonic oscillations provides a good quantitative description of the data and gives estimates for the first two anharmonic terms in an expansion of the sheath potential around the particle equilibrium.

Journal Article↗
PubMed2000

Growth and form of planetary seedlings: results from a microgravity aggregation experiment.

The outcome of the first stage of planetary formation, which is characterized by ballistic agglomeration of preplanetary dust grains due to Brownian motion in the free molecular flow regime of the solar nebula, is still somewhat speculative. We performed a microgravity experiment flown onboard the space shuttle in which we simulated, for the first time, the onset of free preplanetary dust accumulation and revealed the structures and growth rates of the first dust agglomerates in the young solar system. We find that a thermally aggregating swarm of dust particles evolves very rapidly and forms unexpected open-structured agglomerates.

Models, Theoretical↗
PubMed2000

Influence of charge variation on particle oscillations in the plasma sheath

The theory of dust particle oscillations in the plasma sheath is presented, taking into account particle charging kinetics and neutral gas friction. Effects of "regular" and stochastic charge variations are considered. It is shown that whilst regular variations generally enhance the damping of horizontally propagating dust lattice waves, they can also cause an instability in the vertical oscillations of single particles. The stochastic charge variations, if sufficiently strong, result in exponential growth of the mean energy of both types of oscillations.

Journal Article↗
PubMed1998

Discrimination of irritable bowel syndrome by non-linear analysis of 24-h jejunal motility.

Conventional analysis of ambulatory longterm manometry of the small intestine has revealed abnormalities in patients with the irritable bowel syndrome (IBS). The aim was to use methods from non-linear dynamics, in particular the concepts of symbolic dynamics and entropy, in order to discriminate motility in IBS from healthy subjects. 24-h jejunal motility was recorded in 30 IBS patients and 30 healthy subjects. Computerized analysis of contraction amplitudes and intercontractile intervals was performed. Both time series were analysed by symbolic dynamics and entropy to quantify the degree of randomness inherent in the signal. During phase II IBS patients exhibited significantly increased entropies for the intercontractile intervals (IBS: 0.978 +/- 0.016, C: 0.965 +/- 0.020, P = 0.004) and for the contraction amplitudes (IBS: 0.978 +/- 0.008, C: 0.970 +/- 0.026, P = 0.05) compared with healthy subjects. In addition, a significantly increased mean contraction amplitude (mmHg) was found in patients (IBS: 25.2 +/- 4.8, C: 22.2 +/- 3.1, P = 0.003). Considering a combination of both parameters, a diagnostic accuracy of 82% was achieved. We conclude that phase II motility of the small intestine is more random in IBS than in health. Symbolic dynamics seems to be a promising new concept for the analysis of long-term gastrointestinal motility recordings.

Adult↗
PubMed1997

Improving early recognition of malignant melanomas by digital image analysis in dermatoscopy.

The malignant melanoma (MM) is the most dangerous human skin disease. The incidence increased dramatically during the last years. The only chance for the patient is an early recognition and excision of the MM. The best diagnostic method for this is skin surface microscopy or dermatoscopy. Its use, however, requires much expertise. In order to support learning and using the method, a computer-based dermatoscopy workstation is being developed. Among others, new complexity measures are used for the image analysis.

Algorithms↗