Dynamics and stability of directional jumps in the desert locust

Locusts are known for their ability to jump large distances to avoid predation. The jump also serves to launch the adult locust into the air in order to initiate flight. Various aspects of this important behavior have been studied extensively, from muscle physiology and biomechanics, to the energy storage systems involved in powering the jump, and more. Less well understood are the mechanisms participating in control of the jump trajectory. Here we utilise video monitoring and careful analysis of experimental directional jumps by adult desert locusts, together with dynamic computer simulation, in order to understand how the locusts control the direction and elevation of the jump, the residual angular velocities resulting from the jump and the timing of flapping-flight initiation. Our study confirms and expands early findings regarding the instrumental role of the initial body position and orientation. Both real-jump video analysis and simulations based on our expanded dynamical model demonstrate that the initial body coordinates of position (relative to the hind-legs ground-contact points) are dominant in predicting the jumps’ azimuth and elevation angles. We also report a strong linear correlation between the jumps’ pitch-angular-velocity and flight initiation timing, such that head downwards rotations lead to earlier wing opening. In addition to offering important insights into the bio-mechanical principles of locust jumping and flight initiation, the findings from this study will be used in designing future prototypes of a bio-inspired miniature jumping robot that will be employed in animal behaviour studies and environmental monitoring applications.

Investigation of Low Energy Nitrogen Ion Implantation into Gold

Noble metal nitrides have stimulated many theoretical and experimental studies on account of their abnormally high bulk modulus and intriguing electronic properties. Gold surfaces are implanted by the nitrogen ions of low energy in the present work. The surface morphology are observed by atomic force microscopy (AFM).The surface microstructure are studied with X-ray diffraction (XRD). The results of XRD and AFM show weak evidence for the formation of a nano-scale gold nitride. The nitrogen concentration depth profile in gold film has been calculated using a dynamic computer simulation to determine the possible crystal structure of the Au-N system. The mechanisms of gold nitride formation are discussed in the end.

Nitrogen Concentration in N-Implanted Gold on the Formation of Gold Nitride

Although gold nitride has been produced by Siller and co-workers by irradiating a gold film with low energy nitrogen ions, the unsuccessful reason for previous attempts to produce gold nitride is not clear yet. In general, nitrogen concentration depth profile probably influences gold nitride formation. But it is difficult to measure nitrogen concentration depth profile in the N-implanted layer at a low implantation energy of 500 eV. Ion concentration depth profiles in amorphous solids can be determined rather accurately in the case of low implantation fluences using TRIM code. The sputtering effect of ion implantation of high fluences on the concentration depth profile of implanted nitrogen ions should be considered. A dynamic computer simulation based on a TRIDYN code has been applied to calculate nitrogen concentration depth profile in a N-implanted gold film using the different parameters of the fluence and energy in the present work. The sputtering effect of a high fluence on the concentration depth profile can be considered in the TRIDYN simulation. The parameters of fluence and energy that enable to get the gold nitride in thin film are analyzed based on the simulation results. It is put forward some possible ways to improve the formation of gold nitride further.