Sensorimotor control in vertebrates relies on internal models. When extending an arm to reach for an object, the brain uses predictive models of both limb dynamics and target properties. Whether invertebrates use such models remains unclear. Here we examine to what extent prey interception by dragonflies (Plathemis lydia), a behaviour analogous to targeted reaching, requires internal models. By simultaneously tracking the position and orientation of a dragonfly's head and body during flight, we provide evidence that interception steering is driven by forward and inverse models of dragonfly body dynamics and by models of prey motion. Predictive rotations of the dragonfly's head continuously track the prey's angular position. The head-body angles established by prey tracking appear to guide systematic rotations of the dragonfly's body to align it with the prey's flight path. Model-driven control thus underlies the bulk of interception steering manoeuvres, while vision is used for reactions to unexpected prey movements. These findings illuminate the computational sophistication with which insects construct behaviour.
Using techniques developed by Goldschmidt and lately utilized by Foster, solid-state equilibria were studied in the system Mg0-A1203-SiOr Zr02. The ternary systems Mg0-A120rSi02 and Mg0-SiOz-ZrO2 are the only faces of this fourphase system that have beep studied extensively. Compositions in each of the four faces were heated to temperatures below their fusion point and, after they had been cooled, they were examined by X rays to identify the phases present. After solid-state equilibria had been established or verified in the four faces of the system, quaternary compositions were studied to determine the Alkemade tetrahedra.
The differential thermal analysis apparatus described consists of an important improvement. This is the arrangement of the sample and standard holder so that the thermocouples become both the holder and the differential temperature measuring device. This arrangement permits easy removal of the sample and also permits the investigation of exothermic and endothermic reactions at much higher temperatures without damage to the thermocouples.
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