Non-Hamiltonian features of a classical pilot-wave dynamics

A bouncing droplet on a vibrated bath can couple to the waves it generates, so that it becomes a propagative walker. Its propulsion at constant velocity means that a balance exists between the permanent input of energy provided by the vibration and the dissipation. Here we seek a simple theoretical description of the resulting non-Hamiltonian dynamics with a walker immersed in a harmonic potential well. We demonstrate that the interaction with the recently emitted waves can be modeled by a Rayleigh-type friction. The Rayleigh oscillator has well defined attractors. The convergence toward them and their stability is investigated through an energetic approach and a linear stability analysis. These theoretical results provide a description of the dynamics in excellent agreement with the experimental data. It is thus a basic framework for further investigations of wave-particle interactions when memory effects are included.Comment: 10 pages, 6 figure

Self-propulsion and crossing statistics under random initial conditions

We investigate the crossing of an energy barrier by a self-propelled particle described by a Rayleigh friction term. We reveal the existence of a sharp transition in the external force field whereby the amplitude dramatically increases. This corresponds to a saddle point transition in the velocity flow phase space, as would be expected for any type of repulsive force field. We use this approach to rationalize the results obtained by Eddi \emph{et al.} [\emph{Phys. Rev. Lett.} \textbf{102}, 240401 (2009)] who studied the interaction between a drop propelled by its accompanying wave field and a submarine obstacle. This wave particle entity can overcome potential barrier, suggesting the existence of a "macroscopic tunneling effect". We show that the effect of self-propulsion is sufficiently strong to generate crossing of the high energy barrier. By assuming a random distribution of initial angles, we define a probability distribution to cross the potential barrier that matches with the data of Eddi \emph{et al.}. This probability is similar to the one encountered in statistical physics for Hamiltonian systems \textit{i.e.} a Boltzmann exponential law.Comment: 7 pages, 4 figure

Self-organization into quantized eigenstates of a classical wave driven particle

A growing number of dynamical situations involve the coupling of particles or singularities with physical waves. In principle these situations are very far from the wave-particle duality at quantum scale where the wave is probabilistic by nature. Yet some dual characteristics were observed in a system where a macroscopic droplet is guided by a pilot-wave it generates. Here we investigate the behaviour of these entities when confined in a two-dimensional harmonic potential well. A discrete set of stable orbits is observed, in the shape of successive generalized Cassinian-like curves (circles, ovals, lemniscates, trefoils...). Along these specific trajectories, the droplet motion is characterized by a double quantization of the orbit spatial extent and of the angular momentum. We show that these trajectories are intertwined with the dynamical build-up of central wave-field modes. These dual self-organized modes form a basis of eigenstates on which more complex motions are naturally decomposed

A priori checking inconsistencies among strategic constraints for assembly plan generation.

International audienceThis paper is related to the field of assembly plan generation. It describes a new approach to a priori check the consistency of an assembly strategy that is given by the assembly system designers before running an assembly plan generation algorithm. The aim of this work is to improve the assembly plan designer's efficiency by reducing the research space while proving the existence of acceptable solutions. The assembly strategy combined with the product's model implies a set of constraints on the assembly processes. The proposed method determines whether the given assembly strategy produces possible assembly processes. In case of inconsistencies among the strategic constraints, the method will help the designer to identify the contradictory constraints. The set of constraints can be expressed by a Boolean equation. First we present the key concepts and models related to the product, processes and added values in the field of assembly plan generation. Second we define existing strategic constraints, and propose three new ones and a classification of strategic assembly constraints. The originality of the proposed method consists in defining an elementary strategic constraint that is used to describe every other constraint. The proposed method leads to model an assembly strategy by a single Boolean equation that is used to check the inconsistencies. An industrial case study is provided to highlight and to demonstrate the interests of this approach

Control of a team of micro-robots for non-invasive medical applications

National audienceThis paper deals with the control and the synchronisation of a team of micro-robots that performs a non-invasive surgical act into a human body. These micro-robots are very small sized (from ten to some hundred microns). A single unit embeds the minimum of computing power and memory (minimalist electronics) to run a very light program, such as a finite-state machine. The mass effect of the joined micro-robots will allow to achieve the mission through a satisfactory way. The originality of this work being to consider a micro-robot as a disposable unit, which has to be as simple as possible, we need to combine reduced computing power with recent architectures. Some kinds of mission are described and the most promising is detailed. Preliminary simulations support our approach

Unification of the a priori inconsistencies checking among assembly constraints in assembly sequence planning.

International audienceSequence planning generation is an important problem in assembly line design. A good assembly sequence can help to reduce the cost and time of the manufacturing process. This paper focuses on assembly sequence planning (ASP) known as a hard combinatorial optimization problem. Although the ASP problem has been tackled via even more sophisticated optimization techniques, these techniques are often inefficient for proposing feasible assembly sequences that satisfy the assembly planners' preferences. This paper presents an approach that makes easier to check the validity of operations in assembly process. It is based on a model of the assembly planners' preferences by means of strategic constraints. It helps to check a priori the consistency of the assembly constraints (strategic an operative constraints) given by the assembly system designers before and while running an assembly plan generation algorithm. This approach reduces the solution space significantly

New bottom-up algorithm for assembly plan generation : opportunities for micro-factory design.

International audienceThis paper discusses a new approach dedicated to assembly plan generation, called "bottom-up algorithm". It is compared to the traditional "top-down approach", usually used to perform this stage of the design process of the assembly systems for "macro-products". We explore why this new algorithm is better adapted for designing a microassembly system. The case of watch assembly plans generation is described through the both approaches and the obtained results are compared

Modelling the precipitation of NbC on dislocations in a-Fe

A model has been developed for describing the precipitation of NbC on dislocations in ferrite in an Fe–C–Nb steel. This model is a continuous description of the classical laws for nucleation growth and coarsening, which are adapted to the specific case where precipitates only form on dislocations. This model is successfully applied on an extensive data set obtained by small-angle neutron scattering for a wide temperature range and two alloy contents. Using this model, it is possible to estimate the effects of process parameters on the final microstructure and, notably, it is shown that the initial dislocation density has a pronounced influence on the maximum precipitate density

The Effects of an Obesogenic Diet on Liver Oxysterol Metabolism in C57BL/6J Mice

Oxysterols are key regulators of lipid metabolism and play a role in the etiology of atherosclerosis; however, our current understanding of tissue levels of oxysterols during different disease states such as obesity is limited. The purpose of this study was to quantify the effects of obesity induced by a high fat-cholesterol (HFC) diet on liver oxysterol metabolism. Male C57BL/6J mice were fed either a standard control diet (5.0% w/w fat, 0.03% w/w chol) or a HFC (21.0% w/w fat, 0.15% w/w chol) diet for 24 weeks. Comparisons between dietary groups were made with independent sample t-tests. Total body mass and liver tissue mass of the HFC group was greater (33.2±5.2 vs. 49.0±3.6 g and 1.4±0.3 vs. 3.9±0.8 g, respectively; P\u3c0.05) than the control group. In the HFC group, a 3.3 fold increase in lipid mass of the liver tissue was due to increased levels of cholesterol (0.10±0.01 vs. 0.33±0.06 mg/mg protein; P\u3c0.05) and triglyceride (0.37±0.05 vs. 1.49±0.12 mg/mg protein; P\u3c0.05). In the HFC diet, 4β-OH, 5,6β-epoxy, and 27-OH were greater and 7-keto was lower when compared to the control diet. Post-dietary liver 4β-OH, 5,6β-epoxy, and 27-OH were increased in the HFC diet group. Interestingly, despite increased oxysterol levels no significant changes in mRNA levels were observed for oxysterol-related enzymes CYP3A11, CYP27A1 or CYP7A1. The 24-week HFC diet was effective at promoting obesity and hepatic steatosis in mice. Due to the low concentration of oxysterols in the diet, it is unlikely that the oxysterols in the diet had a significant impact on liver oxysterols. Furthermore, our results suggest that the increased hepatic oxysterol levels observed in mice on the obesogenic diet were not due to increased rates of oxysterol synthesis