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Abstract

The analysis of mechanical behaviour of spinal column is until now still a challenge, in spite of the great amount of research which has been conducted over the last years. It is a particularly complex structure considering number of components, their shapes and mechanical characteristics. The objectives of the presented investigations are to understand the mechanisms of the mechanical behaviour of the spine structure and the role of its components, as well as the factors of its dysfunctions as scoliosis discopathy, spondylolisthesis. Also some mechanical effects of surgical interventions by total disc replacement is considered. To account for the 3D character of the spine system including vertebrae, discs, ligaments, muscles etc. the finite element method (FEM) formulation was used throughout the paper. Some specific features of the structure are included in the models as non-conservative loads and muscular tension control performed by the nervous system. The finite element method together with CAD programs and experimental validation was used in investigations of a new type of artificial disc for lumbar spine. The stress analyses were performed for the prostheses being in clinical use and for some original new designs. The conclusions concern most important determinants of the mechanical behaviour of the system and the quality of the intervertebral disc prosthesis.
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Abstract

Oilseed rape (Brassica napus L. ssp. oleifera Metzg) was the subject of the study in two forms: winter cv. 'Muller' (at the rosette stage - the first internode BBCH 30-31) and spring cv. `Feliks' (at the yellow bud stage BBCH 59). The main gas-exchange parameters, net photosynthetic rate (P-N) transpiration rate (E), stomatal conductance (g(s)), and intercellular CO2 concentration (Ci) were measured on leaves prior to the piercing and immediately after the short-term piercing. The effect of mechanical wounding revealed different progress of the gas exchange process for the two forms. Piecewise linear regression with the breakpoint estimation showed that the plants at the same age but at a different vegetal stage, manage mechanical leaf-piercing differently. The differences concerned the stomatal conductance and transpiration changes since for rosette leaves the process consisted of five intervals with a uniform direction, while for stem leaves-of five intervals with a fluctuating direction. These parameters got stabilized within a similar time (220 mins) for both forms. The process of net photosynthetic rate was altered by the plant stages. 'Muller' plants at the rosette stage demonstrated dependence of P-N on time in log-linear progression: y (P-N) = 8.01+ 2.73 log(10) (x t(2)); 7 < t(2) < 220; R-2 = 0.96. For stem leaves of Teliks' plants the process of transpiration, in terms of directions, was convergent with the process of photosynthesis. Those two processes were synchronized from 1st to 114th min of the test (r = 0.85; p < 0.001) in plants at the rosette stage and from 26th to 148th min in stem leaves (r = 0.95; p < 0.001).
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