A set of unified constitutive equations is presented that predict the asymmetric tension and compression creep behaviour and recently observed double primary creep of pre - stretched/naturally aged aluminium - cooper - lithium alloy AA2050 - T34. The evolution of the primary micro - and macro - variables related to the precipitation hardening and creep deformation of the alloy during creep age forming (CAF) are analysed and modelled. E quations for the yield strength evolution of the alloy, including an initial reversi on and subsequent strengthening, ar e proposed based on a theory of concurrent dissolution, re - nucleation and growth of precipitates during artificial ageing . We present new observations of so - called double primary creep during the CAF process . This phenomenon is then predicted by introducing effects of interact ing microstructures , including evolving precipitates, diffusing solutes and dislocations , into the sinh - law creep model. In addition, concepts of threshold creep stress ??? ??? ??? and a microstructu re - dependant creep variable H , which behave differently under different external stress directions, are proposed and incorporat ed into the creep model . This enables predict ion of the asymmetric tension and compression creep - ageing behaviour of the alloy. Q uanti tative transmission electron microscopy (TEM) and related small - angle X - ray scattering (SAXS) analysis ha ve been carried out for selected creep - aged samples to assist the development and calibration of the constitutive model. A good agreement has been achieved between the experimental results and the model. The model has the potential to be applied to creep age form ing of other heat - treatable aluminium alloys
The aim of this randomized, controlled, double-blind study was to examine how the activation pattern of the masseter muscle changes during natural function when experimental pain is induced in a discrete anterior area of the muscle. In 20 subjects, three bipolar surface electrodes and three intramuscular fine-wire electrodes (antero-posterior mapping) were simultaneously attached above and in the right masseter muscle to record the electromyographic (EMG) activity during unilateral chewing before and after infusion of a 0.9% isotonic and 5% hypertonic saline bolus in the anterior area of the muscle. The activity of the contralateral masseter muscle was registered by surface electrodes. In addition, the development of pain intensity was quantitatively measured with a numerical rating scale (NRS). While both saline concentrations caused pain, the hypertonic solution evoked stronger pain. The experiments also provided evidence of a significant although differential activity reduction of the ipsilateral masseter muscle in the antero-posterior direction. The activity reduction decreased with increasing distance from the location of the infusion. The results support the idea that the strategy of differential activation protects the injured muscle while simultaneously maintaining optimal function.
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