Resilience Model for Teams of Autonomous Unmanned Aerial Vehicles (UAV) Executing Surveillance Missions

Teams of low-cost Unmanned Aerial Vehicles (UAVs) have gained acceptance as an alternative for cooperatively searching and surveilling terrains. These UAVs are assembled with low-reliability components, so unit failures are possible. Losing UAVs to failures decreases the team\u27s coverage efficiency and impacts communication, given that UAVs are also communication nodes. Such is the case of a Flying Ad Hoc Network (FANET), where the failure of a communication node may isolate segments of the network covering several nodes. The main goal of this study is to develop a resilience model that would allow us to analyze the effects of individual UAV failures on the team\u27s performance to improve the team\u27s resilience. The proposed solution models and simulates the UAV team using Agent-Based Modeling and Simulation. UAVs are modeled as autonomous agents, and the searched terrain as a two-dimensional M x N grid. Communication between agents permits having the exact data on the transit and occupation of all cells in real time. Such communication allows the UAV agents to estimate the best alternatives to move within the grid and know the exact number of all agents\u27 visits to the cells. Each UAV is simulated as a hobbyist, fixed-wing airplane equipped with a generic set of actuators and a generic controller. Individual UAV failures are simulated following reliability Fault Trees. Each affected UAV is disabled and eliminated from the pool of active units. After each unit failure, the system generates a new topology. It produces a set of minimum-distance trees for each node (UAV) in the grid. The new trees will thus depict the rearrangement links as required after a node failure or if changes occur in the topology due to node movement. The model should generate parameters such as the number and location of compromised nodes, performance before and after the failure, and the estimated time of restitution needed to model the team\u27s resilience. The study addresses three research goals: identifying appropriate tools for modeling UAV scenarios, developing a model for assessing UAVs team resilience that overcomes previous studies\u27 limitations, and testing the model through multiple simulations. The study fills a gap in the literature as previous studies focus on system communication disruptions (i.e., node failures) without considering UAV unit reliability. This consideration becomes critical as using small, low-cost units prone to failure becomes widespread

Influence of virtual reality soccer game on walking performance in robotic assisted gait training for children

BACKGROUND: Virtual reality (VR) offers powerful therapy options within a functional, purposeful and motivating context. Several studies have shown that patients' motivation plays a crucial role in determining therapy outcome. However, few studies have demonstrated the potential of VR in pediatric rehabilitation. Therefore, we developed a VR-based soccer scenario, which provided interactive elements to engage patients during robotic assisted treadmill training (RAGT). The aim of this study was to compare the immediate effect of different supportive conditions (VR versus non-VR conditions) on motor output in patients and healthy control children during training with the driven gait orthosis Lokomat*. METHODS: A total of 18 children (ten patients with different neurological gait disorders, eight healthy controls) took part in this study. They were instructed to walk on the Lokomat in four different, randomly-presented conditions: (1) walk normally without supporting assistance, (2) with therapists' instructions to promote active participation, (3) with VR as a motivating tool to walk actively and (4) with the VR tool combined with therapists' instructions. The Lokomat gait orthosis is equipped with sensors at hip and knee joint to measure man-machine interaction forces. Additionally, subjects' acceptance of the RAGT with VR was assessed using a questionnaire. RESULTS: The mixed ANOVA revealed significant main effects for the factor CONDITIONS (p < 0.001) and a significant interaction CONDITIONS x GROUP (p = 0.01). Tests of between-subjects effects showed no significant main effect for the GROUP (p = 0.592). Active participation in patients and control children increased significantly when supported and motivated either by therapists' instructions or by a VR scenario compared with the baseline measurement "normal walking" (p < 0.001). CONCLUSIONS: The VR scenario used here induces an immediate effect on motor output to a similar degree as the effect resulting from verbal instructions by the therapists. Further research needs to focus on the implementation of interactive design elements, which keep motivation high across and beyond RAGT sessions, especially in pediatric rehabilitation

Virtual reality for enhancement of robot-assisted gait training in children with central gait disorders

Objective: To examine the effect of various forms of training interventions, with and without virtual reality, on the initiation and maintenance of active participation during robot-assisted gait training. Design: Intervention study at the Rehabilitation Centre Affoltern a. A., University Children’s Hospital, Zurich. Subjects: Ten patients (5 males, mean age 12.47 years, standard deviation 1.84 years) with different neurological gait disorders and 14 healthy children (7 males, mean age 11.76 years, standard deviation 2.75 years). Methods: All participants walked in the driven gait orthosis Lokomat® in 4 different randomly-assigned conditions. Biofeedback values calculated during swing phases were the primary outcome measure and secondary outcomes were derived from a questionnaire assessing the participant’s motivation. Results: Findings revealed a significant main effect for training condition in all participants (p<0.001), for patients (p<0.05) and for healthy controls (p<0.01). Overall, both virtual reality-assisted therapy approaches were equally the most effective in initiating the desired active participation in all children, compared with conventional training conditions. Motivation was very high and differed between the groups only in the virtual navigation condition. Conclusion: Novel virtual reality-based training conditions represent a valuable approach to enhance active participation during robot-assisted gait training in patients and healthy controls

Branching fraction and CP asymmetries of B0→KS0KS0KS0

We present measurements of the branching fraction and time-dependent CP-violating asymmetries in B0→K0SK0SK0S decays based on 227×106 Υ(4S)→BB decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We obtain a branching fraction of (6.9+0.9−0.8±0.6)×10−6, and CP asymmetries C=−0.34+0.28−0.25±0.05 and S=−0.71+0.38−0.32±0.04, where the first uncertainties are statistical and the second systematic

Improved measurement of the Cabibbo-Kobayashi-Maskawa angle α using B0(B)→p+p- decays

We present results from an analysis of B0(B¯¯¯0)→ρ+ρ− using 232×106 Υ(4S)→BB¯¯¯ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We measure the longitudinal polarization fraction fL=0.978±0.014(stat)+0.021−0.029(syst) and the CP-violating parameters SL=−0.33±0.24(stat)+0.08−0.14(syst) and CL=−0.03±0.18(stat)±0.09(syst). Using an isospin analysis of B→ρρ decays, we determine the unitarity triangle parameter α. The solution compatible with the standard model is α=(100±13)°

Improved Measurement of the Cabibbo-Kobayashi-Maskawa Angle α Using B0(B¯)→ρ+ρ- Decays

We present results from an analysis of B0(B̅ 0)→ρ+ρ- using 232×106 Υ(4S)→BB̅ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We measure the longitudinal polarization fraction fL=0.978±0.014(stat)+0.021/-0.029(syst) and the CP-violating parameters SL=-0.33±0.24(stat)+0.08/-0.14(syst) and CL=-0.03±0.18(stat)±0.09(syst). Using an isospin analysis of B→ρρ decays, we determine the unitarity triangle parameter α. The solution compatible with the standard model is α=(100±13)°

Branching fraction and CP asymmetries of B0→KS0KS0KS0

We present measurements of the branching fraction and time-dependent CP-violating asymmetries in B0→K0SK0SK0S decays based on 227×106 Υ(4S)→BB decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. We obtain a branching fraction of (6.9+0.9−0.8±0.6)×10−6, and CP asymmetries C=−0.34+0.28−0.25±0.05 and S=−0.71+0.38−0.32±0.04, where the first uncertainties are statistical and the second systematic