References of "Sepulchre, Rodolphe"
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See detailControl of Bimanual Rhythmic Movements: Trading Efficiency for Robustness Depending on the Context
Ronsse, R.; Thonnard, J. L.; Lefevre Philippe et al

in Experimental Brain Research = Experimentelle Hirnforschung = Expérimentation Cérébrale (2008)

This paper investigates how the efficiency and robustness of a skilled rhythmic task compete against each other in the control of a bimanual movement. Human subjects juggled a puck in 2D through impacts ... [more ▼]

This paper investigates how the efficiency and robustness of a skilled rhythmic task compete against each other in the control of a bimanual movement. Human subjects juggled a puck in 2D through impacts with two metallic arms, requiring rhythmic bimanual actuation. The arms kinematics were only constrained by the position, velocity and time of impacts while the rest of the trajectory did not influence the movement of the puck. In order to expose the task robustness, we manipulated the task context in two distinct manners: the task tempo was assigned at four different values (hence manipulating the time available to plan and execute each impact movement individually); and vision was withdrawn during half of the trials (hence reducing the sensory inflows). We show that when the tempo was fast, the actuation was rhythmic (no pause in the trajectory) while at slow tempo, the actuation was discrete (with pause intervals between individual movements). Moreover, the withdrawal of visual information encouraged the rhythmic behavior at the four tested tempi. The discrete versus rhythmic behavior give different answers to the efficiency/robustness trade-off: discrete movements result in energy efficient movements, while rhythmic movements impact the puck with negative acceleration, a property preserving robustness. Moreover, we report that in all conditions the impact velocity of the arms was negatively correlated with the energy of the puck. This correlation tended to stabilize the task and was influenced by vision, revealing again different control strategies. In conclusion, this task involves different modes of control that balance efficiency and robustness, depending on the context. [less ▲]

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See detailContinuous-time susbspace flows related to the symmetric eigenvalue problem
Absil, Pierre-Antoine; Sepulchre, Rodolphe ULg; Mahony, Robert

in Pacific Journal of Optimization (2008), 4(2), 179--194

The classes of continuous-time flows on Rn×p that induce the same flow on the set of p-dimensional subspaces of Rn are described. The power flow is briefly reviewed in this framework, and a subspace ... [more ▼]

The classes of continuous-time flows on Rn×p that induce the same flow on the set of p-dimensional subspaces of Rn are described. The power flow is briefly reviewed in this framework, and a subspace generalization of the Rayleigh quotient flow [Linear Algebra Appl. 368C, 2003, pp. 343–357] is proposed and analyzed. This new flow displays a property akin to deflation in finite time. [less ▲]

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See detailSTABILIZATION OF THREE-DIMENSIONAL COLLECTIVE MOTION
Scardovi, Luca; Leonard, N. E.; Sepulchre, Rodolphe ULg

in Communications in Information and Systems (2008), 8(4), 473-500

This paper proposes a methodology to stabilize relative equilibria in a model of identical, steered particles moving in three-dimensional Euclidean space. Exploiting the Lie group structure of the ... [more ▼]

This paper proposes a methodology to stabilize relative equilibria in a model of identical, steered particles moving in three-dimensional Euclidean space. Exploiting the Lie group structure of the resulting dynamical system, the stabilization problem is reduced to a consensus problem on the Lie algebra. The resulting equilibria correspond to parallel, circular and helical formations. We first derive the stabilizing control laws in the presence of all-to-all communication. Providing each agent with a consensus estimator, we then extend the results to a general setting that allows for unidirectional and time-varying communication topologies. [less ▲]

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See detailSpatial Models of Bistability in Biological Collectives
Paley, Derek; Leonard, Naomi; Sepulchre, Rodolphe ULg et al

in Proceedings of the 46th IEEE Conference on Decision and Control (2007, December)

We explore collective behavior in biological systems using a cooperative control framework. In particular, we study a hysteresis phenomenon in which a collective switches from circular to parallel motion ... [more ▼]

We explore collective behavior in biological systems using a cooperative control framework. In particular, we study a hysteresis phenomenon in which a collective switches from circular to parallel motion under slow variation of the neighborhood size in which individuals tend to align with one another. In the case that the neighborhood radius is less than the circular motion radius, both circular and parallel motion can occur. We provide Lyapunov-based analysis of bistability of circular and parallel motion in a closed-loop system of selfpropelled particles with coupled-oscillator dynamics. [less ▲]

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See detailAutonomous rigid body attitude synchronization
Sarlette, Alain ULg; Sepulchre, Rodolphe ULg; Leonard, Naomi

in Proceedings of the 46th IEEE Conference on Decision and Control (2007, December)

This paper studies some extensions to the decentralized attitude synchronization of identical rigid bodies. Considering fully actuated Euler equations, the communication links between the rigid bodies are ... [more ▼]

This paper studies some extensions to the decentralized attitude synchronization of identical rigid bodies. Considering fully actuated Euler equations, the communication links between the rigid bodies are limited and the available information is restricted to relative orientations and angular velocities. In particular, no leader nor external reference dictates the swarm's behavior. The control laws are derived using two classical approaches of nonlinear control - tracking and energy shaping. This leads to a comparison of two corresponding methods which are currently considered for distributed synchronization - consensus and stabilization of mechanical systems with symmetries. [less ▲]

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See detailConsensus under general convexity
tuna, S. E.; Sepulchre, Rodolphe ULg

in Proceedings of the 46th IEEE Conference on Decision and Control (2007, December)

A method is proposed to characterize contraction of a set through orthogonal projections. For discrete-time multi-agent systems, quantitative estimates of convergence (to a consensus) rate are provided by ... [more ▼]

A method is proposed to characterize contraction of a set through orthogonal projections. For discrete-time multi-agent systems, quantitative estimates of convergence (to a consensus) rate are provided by means of contracting convex sets. Required convexity for the sets that should include the values that the transition maps of agents take is considered in a more general sense than that of Euclidean geometry. [less ▲]

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See detailStabilization of Collective Motion in Three Dimensions : A Consensus Approach
Scardovi, Luca; Leonard, Naomi; Sepulchre, Rodolphe ULg

in Proceedings of 46th IEEE Conference on Decision and Control (2007, December)

This paper proposes a methodology to stabilize relative equilibria in a model of identical, steered particles moving in three- dimensional Euclidean space. Exploiting the Lie group structure of the ... [more ▼]

This paper proposes a methodology to stabilize relative equilibria in a model of identical, steered particles moving in three- dimensional Euclidean space. Exploiting the Lie group structure of the resulting dynamical system, the stabilization problem is reduced to a consensus problem on the Lie algebra. The resulting equilibria correspond to parallel, circular and helical formations. We rst derive the stabilizing control laws in the presence of all-to-all communication. Providing each agent with a consensus estimator, we then extend the results to a general setting that allows for unidirectional and time-varying communication topologies. [less ▲]

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See detailAlternating Spatial Patterns for Coordinated Group Motion
Swain, Daniel T.; Leonard, Naomi Ehrich; Couzin, Iain D. et al

in Proceedings of the 46th IEEE Conference on Decision and Control (2007, December)

Abstract—Motivated by recent observations of fish schools, we study coordinated group motion for individuals with oscillatory speed. Neighbors that have speed oscillations with common frequency, amplitude ... [more ▼]

Abstract—Motivated by recent observations of fish schools, we study coordinated group motion for individuals with oscillatory speed. Neighbors that have speed oscillations with common frequency, amplitude and average but different phases, move together in alternating spatial patterns, taking turns being towards the front, sides and back of the group. We propose a model and control laws to investigate the connections between these spatial dynamics, communication when sensing is range or direction limited, and convergence of coordinated group motions. [less ▲]

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See detailA Hybrid Systems Approach to Trajectory Tracking Control for Juggling Systems
Sanfelice, Ricardo G.; Teel, Andrew R.; Sepulchre, Rodolphe ULg

in Proceedings of the 46th IEEE Conference on Decision and Control (2007, December)

From a hybrid systems point of view, we provide a modeling framework and a trajectory tracking control design methodology for juggling systems. We present the main ideas and concepts in a one degree-of ... [more ▼]

From a hybrid systems point of view, we provide a modeling framework and a trajectory tracking control design methodology for juggling systems. We present the main ideas and concepts in a one degree-of-freedom juggler, which consists of a ball bouncing on an actuated robot. We design a hybrid control strategy that, with only information of the ball’s state at impacts, controls the ball to track a reference rhythmic pattern with arbitrary precision. We extend this hybrid control strategy to the case of juggling multiple balls with different rhythmic patterns. Simulation results for juggling of one and three balls with a single actuated robot are presented. [less ▲]

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See detailElucidating the altered transcriptional programs in breast cancer using independent component analysis
Teschendorff, A. E.; Journee, Michel ULg; Absil, P.-A. et al

in PLoS Computational Biology (2007), 3(8), 1539-1554

The quantity of mRNA transcripts in a cell is determined by a complex interplay of cooperative and counteracting biological processes. Independent Component Analysis ( ICA) is one of a few number of ... [more ▼]

The quantity of mRNA transcripts in a cell is determined by a complex interplay of cooperative and counteracting biological processes. Independent Component Analysis ( ICA) is one of a few number of unsupervised algorithms that have been applied to microarray gene expression data in an attempt to understand phenotype differences in terms of changes in the activation/ inhibition patterns of biological pathways. While the ICA model has been shown to outperform other linear representations of the data such as Principal Components Analysis ( PCA), a validation using explicit pathway and regulatory element information has not yet been performed. We apply a range of popular ICA algorithms to six of the largest microarray cancer datasets and use pathway- knowledge and regulatory- element databases for validation. We show that ICA outperforms PCA and clustering- based methods in that ICA components map closer to known cancer- related pathways, regulatory modules, and cancer phenotypes. Furthermore, we identify cancer signalling and oncogenic pathways and regulatory modules that play a prominent role in breast cancer and relate the differential activation patterns of these to breast cancer phenotypes. Importantly, we find novel associations linking immune response and epithelial - mesenchymal transition pathways with estrogen receptor status and histological grade, respectively. In addition, we find associations linking the activity levels of biological pathways and transcription factors ( NF1 and NFAT) with clinical outcome in breast cancer. ICA provides a framework for a more biologically relevant interpretation of genomewide transcriptomic data. Adopting ICA as the analysis tool of choice will help understand the phenotype - pathway relationship and thus help elucidate the molecular taxonomy of heterogeneous cancers and of other complex genetic diseases. [less ▲]

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See detailOscillator Models and Collective Motion: spatial patterns in the dynamics of engineered and biological networks
Paley, Derek; Leonard, Naomi E.; Sepulchre, Rodolphe ULg et al

in IEEE Control Systems Magazine (2007), 27(4), 89-105

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See detailRhythmic feedback control of a blind planar juggler
Ronsse, R.; Lefevre, Philippe; Sepulchre, Rodolphe ULg

in IEEE Transactions on Robotics (2007), 23(4), 790-802

The paper considers the feedback stabilization of periodic orbits in a planar juggler. The juggler is "blind," i.e, he has no other sensing capabilities than the detection of impact times. The robustness ... [more ▼]

The paper considers the feedback stabilization of periodic orbits in a planar juggler. The juggler is "blind," i.e, he has no other sensing capabilities than the detection of impact times. The robustness analysis of the proposed control suggests that the arms acceleration at impact is a crucial design parameter even though it plays no role in the stability analysis. Analytical results and convergence proofs are provided for a simplified model of the juggler. The control law is then adapted to a more accurate model and validated in an experimental setup. [less ▲]

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See detailQuantitative onvergence analysis of multi-agent systems
tuna, S. E.; Sepulchre, Rodolphe ULg

in Proceedings of the 7th IFAC Symposium on Nonlinear Control Systems (2007, August)

We introduce a characterization of contraction for bounded convex sets. For discrete-time multi-agent systems we provide an explicit upperbound on the rate of convergence to a consensus under the ... [more ▼]

We introduce a characterization of contraction for bounded convex sets. For discrete-time multi-agent systems we provide an explicit upperbound on the rate of convergence to a consensus under the assumptions of contractiveness and (weak) connectedness (across an interval). Convergence is shown to be exponential when either the system of the function characterizing the contraction is linear [less ▲]

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See detailTime-optimal control of a 3-level quantum system and its generalization to an n-level system
Chang, Dong Eui; Sepulchre, Rodolphe ULg

in Proceedings of the 26th American Control Conference (ACC 2007) (2007, July)

We solve the problem of steering a three-level quantum system from one eigen-state to another in minimum time and study its possible extension to the time-optimal control problem for a general n-level ... [more ▼]

We solve the problem of steering a three-level quantum system from one eigen-state to another in minimum time and study its possible extension to the time-optimal control problem for a general n-level quantum system. For the threelevel system we find all optimal controls by finding two types of symmetry in the problem: Z2 × S3 discrete symmetry and S1 continuous symmetry, and exploiting them to solve the problem through discrete reduction and symplectic reduction. We then study the geometry, in the same framework, which occurs in the time-optimal control of a general n-level quantum system. [less ▲]

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See detailStabilization Laws for Collective Motion in Three Dimensions
Scardovi, Luca; Sepulchre, Rodolphe ULg; Leonard, Naomi

in Proceedings of the European Control Conference (2007, July)

This paper proposes a framework for the design of control laws that stabilize relative equilibria in a model of identical, steered particles moving in three-dimensional Euclidean space. Under the ... [more ▼]

This paper proposes a framework for the design of control laws that stabilize relative equilibria in a model of identical, steered particles moving in three-dimensional Euclidean space. Under the assumption of all-to-all communication, the derived control laws only require relative orientations and positions. We extend the obtained results in the presence of limited communication topologies by equipping each agent with a consensus estimator. [less ▲]

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See detailCooperative attitude synchronization in satellite swarms: a consensus approach
Sarlette, Alain ULg; Sepulchre, Rodolphe ULg; Leonard, Naomi

in Proceedings of the 17th IFAC Symposium on Automatic Control in Aerospace (2007, June)

The present paper considers the problem of autonomous synchronization of attitudes in a swarm of spacecraft. Building upon our recent results on consensus on manifolds, we model the spacecraft as ... [more ▼]

The present paper considers the problem of autonomous synchronization of attitudes in a swarm of spacecraft. Building upon our recent results on consensus on manifolds, we model the spacecraft as particles on SO(3) and drive these particles to a common point in SO(3). Unlike the Euler angle or quaternion descriptions, this model suffers no singularities nor double-points. Our approach is fully cooperative and autonomous: we use no leader nor external reference. We present two types of control laws, in terms of applied control torques, that globally drive the swarm towards attitude synchronization: one that requires tree-like or all-to-all inter-satellite communication (most efficient) and one that works with nearly arbitrary communication (most robust). [less ▲]

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See detailStabilization of planar collective motion: All-to-all communication
Sepulchre, Rodolphe ULg; Paley, Derek; Leonard, Naomi Ehrich

in IEEE Transactions on Automatic Control (2007), 52(5), 811-824

This paper proposes a design methodology to stabilize isolated relative equilibria in a model of all-to-all coupled identical particles moving in the plane at unit speed. Isolated relative equilibria ... [more ▼]

This paper proposes a design methodology to stabilize isolated relative equilibria in a model of all-to-all coupled identical particles moving in the plane at unit speed. Isolated relative equilibria correspond to either parallel motion of all particles with fixed relative spacing or to circular motion of all particles with fixed relative phases. The stabilizing feedbacks derive from Lyapunov functions that prove exponential stability and suggest almost global convergence properties. The results of the paper provide a low-order parametric family of stabilizable collectives that offer a set of primitives for the design of higher-level tasks at the group level. [less ▲]

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