Autonomous Exploration and Mapping with RFS Occupancy-Grid SLAM.

This short note addresses the problem of autonomous on-line path-panning for exploration and occupancy-grid mapping using a mobile robot. The underlying algorithm for simultaneous localisation and mapping (SLAM) is based on random-finite set (RFS) modelling of ranging sensor measurements, implemented as a Rao-Blackwellised particle filter. Path-planning in general must trade-off between exploration (which reduces the uncertainty in the map) and exploitation (which reduces the uncertainty in the robot pose). In this note we propose a reward function based on the Rényi divergence between the prior and the posterior densities, with RFS modelling of sensor measurements. This approach results in a joint map-pose uncertainty measure without a need to scale and tune their weights.

Autonomous Multi-Robot Search for a Hazardous Source in a Turbulent Environment.

Finding the source of an accidental or deliberate release of a toxic substance into the atmosphere is of great importance for national security. The paper presents a search algorithm for turbulent environments which falls into the class of cognitive (infotaxi) algorithms. Bayesian estimation of the source parameter vector is carried out using the Rao-Blackwell dimension-reduction method, while the robots are controlled autonomously to move in a scalable formation. Estimation and control are carried out in a centralised replicated fusion architecture assuming all-to-all communication. The paper presents a comprehensive numerical analysis of the proposed algorithm, including the search-time and displacement statistics.

Emulating avian orographic soaring with a small autonomous glider.

This paper explores a method by which an unpowered, fixed-wing micro air vehicle (MAV) may autonomously gain height by utilising orographic updrafts in urban environments. These updrafts are created when wind impinges on both man-made and natural obstacles, and are often highly turbulent and very localised. Thus in contrast to most previous autonomous soaring research, which have focused on large thermals and ridges, we use a technique inspired by kestrels known as 'wind-hovering', in order to maintain unpowered flight within small updrafts. A six-degree-of-freedom model of a MAV was developed based on wind-tunnel tests and vortex-lattice calculations, and the model was used to develop and test a simple cascaded control system designed to hold the aircraft on a predefined trajectory within an updraft. The wind fields around two typical updraft locations (a building and a hill) were analysed, and a simplified trajectory calculation method was developed by which trajectories for height gain can be calculated on-board the aircraft based on a priori knowledge of the wind field. The results of simulations are presented, demonstrating the behaviour of the system in both smooth and turbulent flows. Finally, the results from a series of flight tests are presented. Flight tests at the hill were consistently successful, while flights around the building could not be sustained for periods of more than approximately 20 s. The difficulty of operating near a building is attributable to significant levels of low-frequency unsteadiness (gustiness) in the oncoming wind during the flight tests, effectively resulting in a loss of updraft for sustained periods.

Functional outcomes following total knee arthroplasty: a randomised trial comparing computer-assisted surgery with conventional techniques.

BACKGROUND: A number of trials have shown improved radiological alignment following total knee arthroplasty using computer-assisted surgery (CAS) compared with conventional surgery. Few studies, however, have looked at functional outcomes. METHODS: We prospectively studied a cohort of 107 patients that underwent TKA by a single surgeon. Patients were randomised into 3 groups: computer-assisted surgery for both the femur and the tibia, intramedullary guides for both the femur and the tibia, and an intramedullary guide for the femur and an extramedullary guide for the tibia. Patients were followed-up post-operatively with the Short Form Health Survey (SF-12) and Oxford Knee Score (OKS) questionnaires. RESULTS: At a median follow-up of 46 months (range 30-69 months), there was a trend towards higher OKS results in the CAS group, with a mean score of 40.6 in the CAS group compared to 37.6 in the extramedullary group and 36.8 in the intramedullary group. The difference seen in the OKS between CAS and the conventional groups had a significant unadjusted p-value (0.024), and approached significance when adjusted for age and sex (0.054). There was a significant improvement in the OKS when the mechanical axis was within ±3° of neutral, versus those outside this range (median of 41.0 compared to 38.3, p=0.045). DISCUSSION: This study shows that clinically significant differences are being seen in functional scores of patients treated with CAS versus conventional guides, at medium-term follow up. Our findings reinforce the tenet that a coronal mechanical axis of within 3° of neutral equates to significantly better functional outcomes.