Hybrid HIPIMS and DC magnetron sputtering deposition of TiN coatings: Deposition rate, structure and tribological properties

High power impulse magnetron sputtering (HIPIMS) has the advantage of ultra-dense plasma deposition environment although the resultant deposition rate is significantly low. By using a closed field unbalanced magnetron sputtering system, a hybrid process consisting of one HIPIMS powered magnetron and three DC magnetrons has been introduced in the reactive sputtering deposition of a TiN hard coating on a hardened steel substrate, to investigate the effect of HIPIMS incorporation on the deposition rate and on the microstructure and mechanical and tribological properties of the deposited coating. Various characterizations and tests have been applied in the study, including XRD, FEG-SEM, cross-sectional TEM, Knoop hardness, adhesion tests and unlubricated ball-on-disk tribo-tests. The results revealed that, both the DC magnetron and hybrid-sputtered TiN coatings exhibited dense columnar morphology, a single NaCl-type cubic crystalline phase with strong (220) texture, and good adhesion property. The two coatings showed similar dry sliding friction coefficient of 0.8 – 0.9 and comparable wear coefficient in the range of 1 – 2× 10-15 m3N-1m-1. The overall deposition rate of the hybrid sputtering, being 0.047 μm/min as measured in this study, was governed predominantly by the three DC magnetrons whereas the HIPIMS only made a marginal contribution. However, the incorporated HIPIMS has been found to lead to remarkable reduction of the compressive residual stress from -6.0 to -3.5 GPa and a slight increase in the coating hardness from 34.8 to 38.0 GPa

Integrating swarm intelligence with bayesian networks for continuous UAV-based surveillance in dynamic environments

The loss of wildlife due to illegal poaching activity poses threats on both the survival of iconic animal species and the livelihood of local communities. This research proposes a distributed surveillance model in which a UAV swarm autonomously coordinates continuous surveillance in a dynamic environment. The adaptive behaviour of poachers has the potential to negatively affect surveillance performance and is therefore taken into consideration through the proposed ACOSG model. The novelties of this research are twofold. A mission selection algorithm is proposed that addresses the deficiencies of the existing HAPF-ACO model while improving on surveillance effectiveness. Bayesian learning is applied to dynamically prioritise surveillance efforts of the proposed HAPF-BLACOPS model. Additionally, the learning rate of both poachers and UAVs is analysed to determine whether surveillance remains effective in response to adaptive poacher behaviour. Simulation results show that the proposed model significantly outperforms the current stateof-the-art HAPF-ACO model. Prioritisation of surveillance efforts is achieved through the use of (A)BNs, such that coverage of the target area is reduced by 30%, while maintaining the surveillance effectiveness of the current state-of-the-art. It is found that the interactions between the APF and ACO modules limit the extent to which the (A)BNs’ predictions influence the UAVs’ spatiotemporal patterns and therefore limit the effects of prioritisation on surveillance performance as well. The adaptive capabilities of the poachers and the learning rate of the UAV swarm do not significantly affect surveillance performance and the loss of wildlife, due to a limited amount of newly gained experience. Future research opportunities are identified that can improve the influence of the (A)BN on surveillance performance and prioritisation.Aerospace Engineerin

MESURE DE LA SECTION EFFICACE 12C(γ, xn) DU SEUIL JUSQU'A 33 MeV.

La réaction 12C(γ, xn) a été produite dans une cible de carbone naturel par le rayonnement de freinage du linac. Les photoneutrons sont détectés par un système du type Halpern. La méthode d'analyse de Penfold et Leiss et celle de Cook ont été appliquées. La forme de la résonance géante est conforme à celle observée dans les dernières expériences.The 12C(γ, xn)-reaction was produced in a natural carbon target by the bremsstrahlung beam from the linac. The photoneutrons are detected by a Halpern-type system. Penfold and Leiss' analysis method as well as Cook's method were applied. The shape of the giant resonance is in good agreement with that observed in previous experiments