RESUMO
The purpose of this paper was to study the evolution and dynamic characteristics of the helical gear system co-existence response considering the occurrence of de-meshing and reverse impact under lubrication conditions. The double-three tooth alternate meshing model of a helical gear was established, and the time-varying geometric parameters, motion parameters, and load distribution of positive meshing and reverse impact were analyzed, respectively. The variation of oil film parameters and the coupling between oil film stiffness and meshing stiffness of a gear system were studied according to the equivalent lubrication model of a helical gear. Considering the phenomenon that the meshing state changed from positive meshing to de-meshing and reverse impact, the dynamics model was established. The global bifurcation diagram, the attraction domain, the phase portrait, and the Poincaré section were used to analyze the evolution of a coexistence response and dynamic characteristics with helical gear system parameters.
RESUMO
One mechanism for physiological adjustment of small mammals to different habitats and different seasons is by seasonal acclimatization of their osmoregulatory system. We examined the abilities of broad-toothed field mice (Apodemus mystacinus) from different ecosystems ('sub-alpine' and 'Mediterranean') to cope with salinity stress under short day (SD) and long day (LD) photoperiod regimes. We compared urine volume, osmolarity, urea and electrolyte (sodium, potassium and chloride) concentrations. Significant differences were noted in the abilities of mice from the two ecosystems to deal with salinity load; in particular sub-alpine mice produced less concentrated urine than Mediterranean mice with SD- sub-alpine mice seeming to produce particularly dilute urine. Urea concentration generally decreased with increasing salinity, whereas sodium and potassium levels increased, however SD- sub-alpine mice behaved differently and appeared not to be able to excrete electrolytes as effectively as the other groups of mice. Differences observed provide an insight into the kinds of variability that are present within populations inhabiting different ecosystems, thus how populations may be able to respond to potential changes in their environment. Physiological data pertaining to adaptation to increased xeric conditions, as modelled by A. mystacinus, provides valuable information as to how other species may cope with potential climatic challenges.