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Biomedical subjects

P Kurowski

Publications and source records attributed to P Kurowski.

8 recordsLinked to original sources
PubMed2006

Air bubbles under vertical vibrations.

This paper reports on an experimental study of the splitting instability of an air bubble a few centimetres in diameter placed in a sealed cylindrical cell filled with liquid and submitted to vertical oscillations. The response of the bubble to the oscillations is observed with a high-speed video camera. It is found that the bubble dynamics is closely associated with the acceleration of the cell Gamma. For small acceleration values, the bubble undergoes minor shape deformations. With increasing acceleration values, these deformations are amplified and for sufficiently large Gamma the bubble becomes toroidal. The bubble may then become unstable and split into smaller parts. The onset of bubble division is studied and its dependency on physical parameters such as the fluid viscosity, the fluid surface tension and the initial size of the bubble is presented. It is found that the criterion for the bubble splitting process is associated with a threshold based on the acceleration of the oscillations. Above this threshold, the number of bubbles present in the cell is observed to grow until a final steady state is reached. Data analysis reveals that the final bubble size may be characterized in terms of Bond number.

Journal Article↗
PubMed1986

The relationship of degeneration of the intervertebral disc to mechanical loading conditions on lumbar vertebrae.

Degeneration of lumbar intervertebral discs is typical for the aging process and contributes to common low-back problems. It is likely to influence vertebrae by changing the mechanical interaction within each motion segment. This study focuses on the influence of disc degeneration on the mechanism of load transmission through the lumbar vertebral body. Effective stresses, ways of load transmission and failure modes of vertebral body were examined in cases of healthy and degenerated discs. The stress analysis was performed using the Finite Element Method. For healthy discs, the highest effective stresses were found in the center of bony end-plates. For degenerated discs, they were found in the lateral aspects of the end-plates, in the cortical wall, and also in the vertebral body rims. However, regardless of the disc condition, the highest effective stresses do not occupy the whole thickness of the endplate and/or the cortical wall, but are concentrated near the spongy core. Ways of load transmission through the lumbar vertebral body and modes of eventual damage to it are also strongly influenced by the disc condition.

Aging↗
PubMedDate not supplied

[Muscle stress of rehabilitation-oriented concentric and concentric-eccentric implemented isokinetic training].

The method of lactate diagnostics is used to compare the isokinetic concentric and eccentric work pattern in conjunction with relevant muscular stress. Therefore two training groups performed at isokinetic velocity spectra of 90 degrees/s, 120 degrees/s, 150 degrees/s and 180 degrees/s four series each. The factor "work" was kept identical by performing the same training extent. Over the four series it turned out that the eccentric training group had a continuously higher lactate value of 0.5 mmol/l than the concentric training group used as comparison. The results of both groups gave a similar lactate concentration during practice. Nevertheless it showed that a two minute break is not sufficient to initiate a regeneration process.

Adult↗
PubMedDate not supplied

The importance of mechanical factors in the etiology of spondylolysis. A model analysis of loads and stresses in human lumbar spine.

Because the etiology of spondylolysis is not well understood, the authors performed an analysis of loads and stresses in human lumbar vertebrae to determine whether purely mechanical factors are likely to cause spondylolytic fractures in a normal spine. To perform these studies, modeling methods were applied. A mechanical system was developed to study muscle forces and reactions in joints of the lumbar spine. Next an optimization approach was applied to find loads on vertebrae and muscle forces. Finally photoelastic experiments were performed to find effective stresses and stress concentrations in low lumbar vertebrae. The analysis showed that the highest stresses appear in parts interarticularis. The results prove that factors of a purely mechanical nature are of fundamental importance in the etiology of spondylolysis.

Humans↗