An Architecture for Autonomy

International audienceAn autonomous robot offers a challenging and ideal field for the study of intelligent architectures. Autonomy within a rational behavior could be evaluated by the robot's effectiveness and robustness in carrying out tasks in different and ill-known environments_ It raises major requirements on the control architecture. Furthermore, a robot as a programmable machine brings up other architectural needs, such as the ease and quality of its speci_cation and programming. This paper describes an integrated architecture allowing a mobile robot to plan its tasks, taking into account temporal and domain constraints, to perform corresponding actions and to control their execution in real_time, while being reactive to possible events. The general architecture is composed of three levels : a decision level, an execution level and a functional level. The later is composed of modules that embed the functions achieving sensor data processing and effector control. The decision level is goal and event driven, it may have several layers, according to the application ; their basic structure is a planner/supervisor pair that enables to integrate deliberation and reaction. The proposed architecture relies naturally on several representations, programming paradigms and processing approaches meeting the precise requirements specified for each level. We developed proper tools to meet these specifications and implement each level of the architecture : IxTeT a temporal planner, PRS a procedural system for task refinement and supervision, Kheops for the reactive control of the functional level, and GenoM for the specification and integration of modules at that level. Validation of temporal and logical properties of the reactive parts of the system, through these tools, are presented. Instances of the proposed architecture have been already integrated into several indoor and outdoor robots. Examples from real world experimentations are provided and analyzed

Chain length-dependent cooperativity in fatty acid binding and oxidation by cytochrome P450BM3 (CYP102A1)

Fatty acid binding and oxidation kinetics for wild type P450(sub)BM3 (CYP102A1) from Bacillus megaterium have been found to display chain length-dependent homotropic behavior. Laurate and 13-methyl-myristate display Michaelis-Menten behavior while there are slight deviations with myristate at low ionic strengths. Palmitate shows Michaelis-Menten kinetics and hyperbolic binding behavior in 100 mmol/L phosphate, pH 7.4, but sigmoidal kinetics (with an apparent intercept) in low ionic strength buffers and at physiological phosphate concentrations. In low ionic strength buffers both the heme domain and the full-length enzyme show complex palmitate binding behavior that indicates a minimum of four fatty acid binding sites, with high cooperativity for the binding of the fourth palmitate molecule, and the full-length enzyme showing tighter palmitate binding than the heme domain. The first flavin-to-heme electron transfer is faster for laurate, myristate and palmitate in 100 mmol/L phosphate than in 50mmol/L Tris (pH 7.4), yet each substrate induces similar high-spin heme content. For palmitate in low phosphate buffer concentrations, the rate constant of the first electron transfer is much larger than k(sub)cat. The results suggest that phosphate has a specific effect in promoting the first electron transfer step, and that P450(sub)BM3 could modulate Bacillus membrane morphology and fluidity via palmitate oxidation in response to the external phosphate concentration.Benjamin Rowlatt, Jake A. Yorke, Anthony J. Strong, Christopher J. C. Whitehouse, Stephen G. Bell, Luet-Lok Won