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This paper focuses on the analysis of the performance of specific 'detection and labeling' and 'pose estimation' algorithms within a Machine Vision (MV)-based approach for the problem of Autonomous Aerial Refueling (AAR) of UAVs. A robust 'detection and labeling algorithm' for the correct identification and sorting of the optical markers is proposed; a sorted list of marker positions is then provided as input to the 'pose estimation' algorithm. A detailed study of the performance of two specific 'pose estimation' algorithms (GLSDC and LHM) is performed with special emphasis on the required computational effort as well as on the robustness and error propagation characteristics. Extensive simulation studies demonstrate the performance of the LHM and GLSDC algorithms and show the importance of a robust 'detection and labeling' algorithm. The simulation effort is performed using a detailed modeling of the AAR maneuver according to the USAF refueling method

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Airway closure and gas trapping can occur during lung deflation and inflation when fluid menisci form across the lumina of respiratory passageways. Previous analyses of the behavior of liquid in airways have assumed that the airway is completely wetted or that the contact angle of the liquid-gas interface with the airway wall is 0 degrees, and thus that the airway fluid forms an axisymmetric surface. However, some investigators have suggested that liquid in the airways is discontinuous and that contact angles can be as high as 67 degrees. In this study we consider the characteristics of constant curvature surfaces that could form a stable liquid-gas interface in a cylindrical airway. Our analysis suggests that, for small liquid volumes, asymmetric droplets are more likely to form than axisymmetric toroids. In addition, if the fluid contact angle is greater than 13 degrees, asymmetric droplets can sustain larger liquid volumes than axisymmetric toroids before collapsing to form menisci. These results suggest that (1) fluid formations other than axisymmetric toroids could occur in the airways; and (2) the analysis of the behavior of fluids and the development of liquid menisci within the lungs should include the potential role of asymmetric droplets.