In this paper, we present a distributed control strategy, enabling agents to converge onto and travel along a consensually selected curve among a class of closed planar curves. Individual agents identify the number of neighbors within a finite circular sensing range and obtain information from their neighbors through local communication. The information is then processed to update the control parameters and force the swarm to converge onto and circulate along the aforementioned planar curve. The proposed mathematical framework is based on stochastic differential equations driven by white Gaussian noise (diffusion processes). Using this framework, there is maximum probability that the swarm dynamics will be driven toward the consensual closed planar curve. In the simplest configuration where a circular consensual curve is obtained, we are able to derive an analytical expression that relates the radius of the circular formation to the agent's interaction range. Such an intimate relation is also illustrated numerically for more general curves. The agent-based control strategy is then translated into a distributed Braitenberg-inspired one. The proposed robotic control strategy is then validated by numerical simulations and by implementation on an actual robotic swarm. It can be used in applications that involve large numbers of locally interacting agents, such as traffic control, deployment of communication networks in hostile environments, or environmental monitoring.

Background: Augmented reality (AR) allows the surgeon to represent holographic patient-specific anatomical information and surgical instruments in the physical world. To correctly superimpose virtual and physical objects, a hand-eye (HE) calibration method for mapping the virtual and physical spaces was proposed.Methods: Mathematical relationships between the virtual camera and the physical space were derived. Finally, the accuracy and robustness of the proposed HE calibration method were qualitatively and quantitatively evaluated. Results:The proposed calibration method allows us to determine an optimal invariant spatiotemporal mapping between the virtual camera and the physical space. Conclusion:Qualitatively and quantitatively reliable and accurate estimates for the physical-virtual mapping transformation were verified. Consequently, imaging data and surgical instruments holograms can be precisely represented in the physical space.

No abstract

A methodology, which can be classified as Top-Down, aimed at computing technical losses in distribution systems is proposed. It can be applied to either evaluate part of the network or to analyze the whole distribution system. This methodology basically requires the load curve of the studied feeder or substation, and, depending on the analyzed segment, some complementary data. Thus, the contribution of this proposal becomes significant when compared to other methodologies that commonly require large and updated databases, often not available. The proposed technique was applied to two real Brazilian distribution systems. Results, compared with measured data, show the effectiveness of the methodology in computing losses by segments and for the whole circuit.

Background. Our knowledge of mandibular growth mostly derives from cephalometric radiography, which has inherent limitations due to the two-dimensional (2D) nature of measurement. Objective. To assess 3D morphological changes occurring during growth in a rabbit mandible. Methods. Serial cone-beam computerised tomographic (CBCT) images were made of two New Zealand white rabbits, at baseline and eight weeks after surgical implantation of 1 mm diameter metallic spheres as fiducial markers. A third animal acted as an unoperated (no implant) control. CBCT images were segmented and registered in 3D (Implant Superimposition and Procrustes Method), and the remodelling pattern described used color maps. Registration accuracy was quantified by the maximal of the mean minimum distances and by the Hausdorff distance. Results. The mean error for image registration was 0.37 mm and never exceeded 1 mm. The implant-based superimposition showed most remodelling occurred at the mandibular ramus, with bone apposition posteriorly and vertical growth at the condyle. Conclusion. We propose a method to quantitatively describe bone remodelling in three dimensions, based on the use of bone implants as fiducial markers and CBCT as imaging modality. The method is feasible and represents a promising approach for experimental studies by comparing baseline growth patterns and testing the effects of growth-modification treatments.