Comparative Study of Spectral Sensitivity, Irradiance Sensitivity, Spatial Resolution and Temporal Resolution in the Visual Systems of Aratus pisonii and Ocypode quadrata

Autrum’s studies (1950, 1958) on terrestrial arthropods first revealed that the visual systems of arthropods reflected their lifestyles and habitats, demonstrating that rapidly moving predatory diurnal species tend to have better temporal resolution than slower moving nocturnal species. In order to test Autrum’s hypothesis that visual adaptions are driven by predator/prey interactions, the visual physiology of a nocturnal fast-moving predatory crab, the Atlantic ghost crab (Ocypode quadrata), and a diurnal herbivorous crab, the mangrove tree crab (Aratus pisonii), was examined and compared. Spectral sensitivity, irradiance sensitivity, and temporal resolution of the crabs were quantified using the electroretinogram (ERG), while the spatial resolution was calculated utilizing morphological methods. Both O. quadrata and A. pisonii had a single dark-adapted spectral sensitivity peak (494 and 499 nm respectively) and chromatic adaptation had no effect on their spectral sensitivity, indicating that both species have monochromatic visual systems. The temporal resolution of O. quadrata was not significantly different from that of A. pisonii, but O. quadrata did possess a significantly greater spatial resolution and irradiance sensitivity. Both species possess an acuity zone in the anterior region of their eyes. The data presented in this study will aid in the current understanding of the correlation between visual physiology and the life history of the animal

Mitigation techniques for acoustic noise and vibration in switched reluctance drives

PhD ThesisSwitched reluctance machines (SRM) have become an attractive rotating electrical machine in many applications because they have no permanent magnets, have robust structures and high fault tolerance. However, the crucial drawback of the SRM that limits the range of applications, is the acoustic noise and vibration often associated with this technology. The major source of vibration comes from the high deformation of the SRM stator stack, caused primarily by high radial magnetic forces. Vibration behaviour of di erent SRM topologies is analyzed by using nite element software to calculate the magnitude, mode shape and the resonant frequencies of the SRM. This includes determination of the generating magnetic force characteristic for each topology. To improve the accuracy of the vibration model of the SRM stator, which is built from laminated steel sheet, calculation of the mechanical material properties of the stator are developed for structural simulations. The simulation and testing results of the resonant frequency of the SRM are compared to determine the accuracy of the simulation model. There are two main strategies for reducing the vibration in an SRM. I) structural design and II) control technique. In this thesis, the structural design of six types of SRM segmented stator, each shrink- tted into an aluminium housing, are investigated, both in terms of the structural sti ness and resonant frequency. The impact of varying temperature on the resonant frequency of the stator is tested to show the rate of change of the resonant frequency and damping ratio of the stator structure. Furthermore, the control technique of the SRM has also been shown to have a signi cant impact on the vibration produced in the SRM. Improvement of the control technique based on an active vibration cancellation (AVC) method is implemented under load conditions with di erent operating speeds of the SRM and compared with the conventional control method.Royal Thai governmen