Learning walks in an Australian desert ant, Melophorus bagoti

The Central Australian ant Melophorus bagoti is the most thermophilic ant in Australia and forages solitarily in the summer months during the hottest period of the day. For successful navigation, desert ants of many species are known to integrate a path and learn landmark cues around the nest. Ants perform a series of exploratory walks around the nest before their first foraging trip, during which they are presumed to learn about their landmark panorama. Here, we studied 15 naïve M. bagoti ants transitioning from indoor work to foraging outside the nest. In three to four consecutive days, they performed 3 to 7 exploratory walks before heading off to forage. Naïve ants increased the area of exploration around the nest and the duration of trips over successive learning walks. In their first foraging walk, the majority of the ants followed a direction explored on their last learning walk. During learning walks, the ants stopped and performed stereotypical orientation behaviours called pirouettes. They performed complete body rotations with stopping phases as well as small circular walks without stops known as voltes. After just one learning walk, these desert ants could head in the home direction from locations 2 m from the nest, although not from locations 4 m from the nest. These results suggest gradual learning of the visual landmark panorama around the foragers’ nest. Our observations show that M. bagoti exhibit similar characteristics in their learning walks as other desert ants of the genera Ocymyrmex and Cataglyphis.

Modelling of Energy Accumulation in Belt Conveyor Systems Under Faulty Conditions

The consideration of potential energy stored in a system is paramount to carry on safe maintenance operations of mechanical system. In particular, this paper concentrates on the elastic energy accumulation occurring in a belt conveyor system ensuing a seizure of one of the pulleys owing to, for example, dirt and spilled bulk material accumulation in the belt inlet zone. The hazard of considering the system completely discharged just because the electrical supply cut off and the effect of such an energy storage are investigated by means of a lumped mass dynamic mathematical model. It allows time variable operating conditions to be considered, as well as starting and stopping phases transients. Standard maintenance operations are simulated, and the effect of stored energy sudden release investigated.

A new asymptotic method for the modeling of near-field accelerograms

We study high-frequency radiation from a dislocation model of rupture propagation at the earthquake source. We demonstrate that in this case all the radiation emanates from the rupture front and, by a change of variables, that at any instant of time the high-frequency waves reaching an observer come from a line on the fault plane that we call isochrone. An asymptotic approximation to near-source velocity and acceleration is obtained that involves a simple integration along the isochrones for every time step. It is shown that wave front discontinuities (critical or stopping phases) are radiated every time an isochrone becomes tangent to a barrier. This leads to what we call the critical ray approximation which is given in a closed form. The previous results are compared with discrete wavenumber synthetics obtained by Bouchon (1982) for the Gilroy 6 recording of the Coyote Lake earthquake of 1980. The fit between the asymptotic and full numerical method is extremely good. The critical ray approximation permits the identification of different phases in Bouchon's synthetics and the prediction of the behavior of the signal in the vicinity of their arrival time.