Resin composites may be polymerized according to one of several light-curing modes. These modes include variations in intensity of the curing lights and time delay before final cure. The so-called pulse-delay method has earlier been found to reduce the formation of gaps due to polymerization contraction, without mechanical properties of the resin composite being compromised. It was hypothesized that the slow pre-cure of this method would give rise to a different polymer structure than results when the polymer is cured in one step at high intensity. It was found that although the quantity of remaining double bonds was unaffected, the pulse-delay technique led to polymers of increased susceptibility to softening in ethanol. The softness increased with the intensity of the pre-cure and with the waiting time before final cure. The increased softening may be interpreted as the manifestation of a polymer structure having fewer crosslinks.
The question, if muscles can absorb and temporarily store mechanical energy in the form of elastic energy for later re‐use, was studied by having subjects perform maximal vertical jumps on a registering force‐platform. The jumps were performed 1) from a semi‐squatting position, 2) after a natural counter‐movement from a standing position, or 3) in continuation of jumps down from heights of 0.23, 0.40, or 0.69 m. The heights of the jumps were calculated from the registered flight times. The maximum energy level, Eneg, of the jumpers prior to the upward movement in the jump, was considered to be zero in condition 1. In condition 2 it was calculated from the force‐time record of the force‐platform; and in condition 3 it was calculated from the height of the downward jump and the weight of the subject. The maximum energy level after take‐off, Ep0s, was calculated from the height of the jump and the jumper's weight. It was found that the height of the jump and Epos increased with increasing amounts of Eneg, up to a certain level (jumping down from 0.40 m). The gains in Epos over that in condition 1, were expressed as a percentage of Eneg and found to be 22.9 % in condition 2, and 13.2, 10.5, and 3.3 % in the three situations of condition 3. It is suggested that the elastic energy is stored in the active muscles, and it is demonstrated that the muscles of the legs are activated in the downward jumps before contact with the platform is established.
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