Stagewise Newton Method for Dynamic Game Control with Imperfect State Observation

International audienceIn this letter, we study dynamic game optimal control with imperfect state observations and introduce an iterative method to find a local Nash equilibrium. The algorithm consists of an iterative procedure combining a backward recursion similar to minimax differential dynamic programming and a forward recursion resembling a risksensitive Kalman smoother. A coupling equation renders the resulting control dependent on the estimation. In the end, the algorithm is equivalent to a Newton step but has linear complexity in the time horizon length. Furthermore, a merit function and a line search procedure are introduced to guarantee convergence of the iterative scheme. The resulting controller reasons about uncertainty by planning for the worst case disturbances. Lastly, the low computational cost of the proposed algorithm makes it a promising method to do output-feedback model predictive control on complex systems at high frequency. Numerical simulations on realistic robotic problems illustrate the risk-sensitive behavior of the resulting controller

Is the meiofauna a good indicator for climate change and anthropogenic impacts?

Our planet is changing, and one of the most pressing challenges facing the scientific community revolves around understanding how ecological communities respond to global changes. From coastal to deep-sea ecosystems, ecologists are exploring new areas of research to find model organisms that help predict the future of life on our planet. Among the different categories of organisms, meiofauna offer several advantages for the study of marine benthic ecosystems. This paper reviews the advances in the study of meiofauna with regard to climate change and anthropogenic impacts. Four taxonomic groups are valuable for predicting global changes: foraminifers (especially calcareous forms), nematodes, copepods and ostracods. Environmental variables are fundamental in the interpretation of meiofaunal patterns and multistressor experiments are more informative than single stressor ones, revealing complex ecological and biological interactions. Global change has a general negative effect on meiofauna, with important consequences on benthic food webs. However, some meiofaunal species can be favoured by the extreme conditions induced by global change, as they can exhibit remarkable physiological adaptations. This review highlights the need to incorporate studies on taxonomy, genetics and function of meiofaunal taxa into global change impact research

Crocoddyl: An Efficient and Versatile Framework for Multi-Contact Optimal Control

International audienceWe introduce Crocoddyl (Contact RObot COntrol by Differential DYnamic Library), an open-source framework tailored for efficient multi-contact optimal control. Crocoddyl efficiently computes the state trajectory and the control policy for a given predefined sequence of contacts. Its efficiency is due to the use of sparse analytical derivatives, exploitation of the problem structure, and data sharing. It employs differential geometry to properly describe the state of any geometrical system, e.g. floating-base systems. We have unified dynamics, costs, and constraints into a single concept-action-for greater efficiency and easy prototyping. Additionally, we propose a novel multiple-shooting method called Feasibility-prone Differential Dynamic Programming (FDDP). Our novel method shows a greater globalization strategy compared to classical Differential Dynamic Programming (DDP) algorithms, and it has similar numerical behavior to state-of-the-art multiple-shooting methods. However, our method does not increase the computational complexity typically encountered by adding extra variables to describe the gaps in the dynamics. Concretely, we propose two modifications to the classical DDP algorithm. First, the backward pass accepts infeasible state-control trajectories. Second, the rollout keeps the gaps open during the early "exploratory" iterations (as expected in multiple-shooting methods). We showcase the performance of our framework using different tasks. With our method, we can compute highly-dynamic maneuvers for legged robots (e.g. jumping, front-flip) in the order of milliseconds

Evaluation of a pro-recovery training intervention (REFOCUS-RETAFORM) in specialist mental health services across France: stepped-wedge cluster randomised controlled trial protocol

BackgroundWhile recovery orientation is national policy in many countries, evidence remains limited for the effectiveness at a service level. This paper describes the protocol for implementing a pro-recovery training intervention (REFOCUS-RETAFORM) in specialist mental health services across France. The aim is to evaluate whether REFOCUS-RETAFORM plus usual care leads to improved outcomes for adolescent and adult mental health service users compared with usual care alone.MethodsA two-step stepped wedge cluster randomised controlled trial will be conducted, with a nested qualitative sub-study exploring stakeholders’ views on changes in staff-user relationships and implementation influences. The REFOCUS-RETAFORM intervention is a training intervention for mental health staff, to develop recovery-promoting relationships and pro-recovery working practices. Clusters are services, which transition sequentially from control to intervention condition in a randomised order. Eight clusters are randomised to deliver REFOCUS-RETAFORM in year one and eight clusters in year two. Each cluster delivers REFOCUS-RETAFORM to two teams from their organisation (32 teams in total). Participants are a) service users aged 13–65 years attending services implementing REFOCUS-RETAFORM, and b) staff receiving the intervention. The primary outcome is the Questionnaire about the Process of Recovery. Secondary outcomes include perceived stigma and coercion, self-stigma and wellbeing for service users, and recovery-orientation for staff. Data will be collected from 540 service users (180 at baseline, 180 at month 12, 180 at month 24) and 220 staff. We will use multilevel mixed-effects models, adjusting for secular trends and thematic analysis for the qualitative interview data.DiscussionFindings will inform the continued transformation of French specialist mental health services toward a recovery orientation

EVIAN (EAU MINERALE ET THERMALISME)

LYON1-BU Santé (693882101) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

On the Derivation of the Contact Dynamics in Arbitrary Frames: Application to Polishing with Talos

International audienceContact dynamics relies on the simultaneous satisfaction of constraints at the robot body level and at the contact level. At both levels, various formulations can be chosen that all must lead to the same results, given the same hypothesis, hence the little importance of their details. Yet when using it in an optimal control problem, a particular formulation is often imposed by the task to be performed by the robot. In this paper, we detail the formulation of the contact quantities (force, movement) in an arbitrary frame imposed by the task. In that case, we will show that we are typically not interested in working in the local frame (attached to the robot contact point), nor in the world frame, but in a user-defined frame centered at the contact location with a fixed orientation in the world. The derivations can then be used for 6D, 3D or normal (pure-sliding) contact. We implemented the corresponding derivatives on top of the contact dynamics of Pinocchio in the optimal control solver Crocoddyl. We show that a unique formulation is able to handle several operational orientations by achieving several surfacing tasks in model predictive control with the robot Talos

On the Derivation of the Contact Dynamics in Arbitrary Frames: Application to Polishing with Talos

International audienceContact dynamics relies on the simultaneous satisfaction of constraints at the robot body level and at the contact level. At both levels, various formulations can be chosen that all must lead to the same results, given the same hypothesis, hence the little importance of their details. Yet when using it in an optimal control problem, a particular formulation is often imposed by the task to be performed by the robot. In this paper, we detail the formulation of the contact quantities (force, movement) in an arbitrary frame imposed by the task. In that case, we will show that we are typically not interested in working in the local frame (attached to the robot contact point), nor in the world frame, but in a user-defined frame centered at the contact location with a fixed orientation in the world. The derivations can then be used for 6D, 3D or normal (pure-sliding) contact. We implemented the corresponding derivatives on top of the contact dynamics of Pinocchio in the optimal control solver Crocoddyl. We show that a unique formulation is able to handle several operational orientations by achieving several surfacing tasks in model predictive control with the robot Talos