A Lyapunov approach for the exponential stability of a damped Timoshenko beam

In this technical note, we consider the stability properties of a viscously damped Timoshenko beam equation with spatially varying parameters. With the help of the port-Hamiltonian framework, we first prove the existence of solutions and show, by an appropriate Lyapunov function, that the system is exponentially stable and has an explicit decay rate. The explicit exponential bound is computed for an illustrative example of which we provide some numerical simulations

Design principles for long-range energy transfer at room temperature

Typical room temperature conditions hinder ballistic long-range transfer of excitations, rendering quantum phenomena unimportant as potential tools for the design of efficient and controllable energy transfer over significant time and length scales. However, it is well-known that many properties of macroscopic systems depend on the quantum properties of minimal repeating units and, as we show here, excitonic energy transfer is no exception. With the support of an exactly solvable model, we are able to show how exciton delocalization and the ensuing formation of dark states within unit cells can be harnessed to support classical propagation over macroscopic distances. We specifically discuss the role of such factors in nano-fabricated arrays of bacterial photosynthetic complexes via extensive simulations. This allows us to resolve the to-date unexplained experimental observation of exciton diffusion lengths in such arrays in terms of an interplay between intra-unit cell thermalization and delocalization, which conspire to create and use robust dark states at room temperature.Comment: Revised presentation and new title, main results unchanged, 11+10 pages, 3+5 figure

Drug waste minimisation and cost-containment in Medical Oncology: Two-year results of a feasibility study

<p>Abstract</p> <p>Background</p> <p>Cost-containment strategies are required to face the challenge of rising drug expenditures in Oncology. Drug wastage leads to economic loss, but little is known about the size of the problem in this field.</p> <p>Methods</p> <p>Starting January 2005 we introduced a day-to-day monitoring of drug wastage and an accurate assessment of its costs. An internal protocol for waste minimisation was developed, consisting of four corrective measures: 1. A rational, per pathology distribution of chemotherapy sessions over the week. 2. The use of multi-dose vials. 3. A reasonable rounding of drug dosages. 4. The selection of the most convenient vial size, depending on drug unit pricing.</p> <p>Results</p> <p>Baseline analysis focused on 29 drugs over one year. Considering their unit price and waste amount, a major impact on expense was found to be attributable to six drugs: cetuximab, docetaxel, gemcitabine, oxaliplatin, pemetrexed and trastuzumab. The economic loss due to their waste equaled 4.8% of the annual drug expenditure. After the study protocol was started, the expense due to unused drugs showed a meaningful 45% reduction throughout 2006.</p> <p>Conclusion</p> <p>Our experience confirms the economic relevance of waste minimisation and may represent a feasible model in addressing this issue.</p> <p>A centralised unit of drug processing, the availability of a computerised physician order entry system and an active involvement of the staff play a key role in allowing waste reduction and a consequent, substantial cost-saving.</p

Cell Cycle-Dependent Induction of Homologous Recombination by a Tightly Regulated I-SceI Fusion Protein

Double-strand break repair is executed by two major repair pathways: non-homologous end joining (NHEJ) and homologous recombination (HR). Whereas NHEJ contributes to the repair of ionizing radiation (IR)-induced double strand breaks (DSBs) throughout the cell cycle, HR acts predominantly during the S and G2 phases of the cell cycle. The rare-cutting restriction endonuclease, I-SceI, is in common use to study the repair of site-specific chromosomal DSBs in vertebrate cells. To facilitate analysis of I-SceI-induced DSB repair, we have developed a stably expressed I-SceI fusion protein that enables precise temporal control of I-SceI activation, and correspondingly tight control of the timing of onset of site-specific chromosome breakage. I-SceI-induced HR showed a strong, positive linear correlation with the percentage of cells in S phase, and was negatively correlated with the G1 fraction. Acute depletion of BRCA1, a key regulator of HR, disrupted the relationship between S phase fraction and I-SceI-induced HR, consistent with the hypothesis that BRCA1 regulates HR during S phase

Modélisation et analyse de stabilité de robots flexibles : une approche Hamiltonien à ports à paramètres distribués

L'objectif de cette thèse est de fournir un cadre mathématique permettant d'expliciter les modèles dynamiques d'une classe de mécanismes flexibles, de concevoir des lois de commandes adaptée et d'analyser le comportement asymptotique en boucle fermée qui en résulte. D'un point de vue mathématique, les parties flexibles sont décrites par des équations aux dérivée partielles (EDP), alors que la dynamique des parties rigides est décrite par des équations aux dérivée ordinaires (EDO). Par conséquent, le modèle global est décrit par un ensemble mixte de EDO-EDP (m-EDO-EDP), que en cette thèse est etudié en utilisant l'approche hamiltonienne à ports combinée à la théorie des semi-groupes.Tout d'abord, nous définissons une procédure rigoureuse basée sur le principe de moindre action afin d'établir le modèle des mécanismes avec d'éventuels composants flexibles, en fournissant plusieurs exemples illustratifs. Les parties à paramètres distribuées sont modélisées comme des systèmes de contrôle frontière unidimensionnels.Dans un second temps, différentes lois de commande stabilisantes sont synthétisées sur une classe de systèmes m-EDP-EDO linéaires. Les lois de commande proposées permettent d'atteindre une stabilité asymptotique ou exponentielle.Enfin, nous nous intéressons au problème de contact entre un bras rotatif et son environnement dans le cas où le système en rotation est considéré comme étant rigide ou flexible. Puisque ce système présente des changements instantanés dans les temps d'impact, nous étudions ce problème à l'aide de la théorie de commutation appliquée à des systèmes de dimensions infinie.The objective of this thesis is to provide a mathematical framework that allows to explicit the dynamical model of a class of flexible mechanisms, to design their control law and to analyze the resulting closed loop asymptotic behaviour. From a mathematical point of view, the flexible parts are distributed parameter systems whose dynamics are described by Partial Differential Equations (PDE), while the dynamics of the rigid parts are described by Ordinary Differential Equation (ODE). Therefore, the total model is described by a mixed set of ODE-PDE (m-PDE-ODE). For studying these dynamic models, this thesis uses the port-Hamiltonian framework combined with the infinite-dimensional semigroup theory.First, we define a rigorous procedure based on the Least Action Principle for deriving the model of mechanisms with possible flexible components, providing several illustrative examples. The general class of nonlinear systems enclosing all the proposed examples is shown to be passive with respect to its mechanical energy. In this class of systems, the distributed parameter parts are modelled as one dimensional boundary control systems.Second, we restrict ourselves to a linear class of m-ODE-PDE systems for which we propose different control laws. We show that the proposed control laws allow achieving asymptotic or exponential stability.Finally, a rotating arm that enters in contact with the external environment is studied in case the link is considered as being both rigid or flexible. Since this system exhibits instant changes in the impact times, we study this problem with the help of switching theory applied to infinite dimensional systems

Modélisation et analyse de stabilité de robots flexibles : une approche Hamiltonien à ports à paramètres distribués

The objective of this thesis is to provide a mathematical framework that allows to explicit the dynamical model of a class of flexible mechanisms, to design their control law and to analyze the resulting closed loop asymptotic behaviour. From a mathematical point of view, the flexible parts are distributed parameter systems whose dynamics are described by Partial Differential Equations (PDE), while the dynamics of the rigid parts are described by Ordinary Differential Equation (ODE). Therefore, the total model is described by a mixed set of ODE-PDE (m-PDE-ODE). For studying these dynamic models, this thesis uses the port-Hamiltonian framework combined with the infinite-dimensional semigroup theory.First, we define a rigorous procedure based on the Least Action Principle for deriving the model of mechanisms with possible flexible components, providing several illustrative examples. The general class of nonlinear systems enclosing all the proposed examples is shown to be passive with respect to its mechanical energy. In this class of systems, the distributed parameter parts are modelled as one dimensional boundary control systems.Second, we restrict ourselves to a linear class of m-ODE-PDE systems for which we propose different control laws. We show that the proposed control laws allow achieving asymptotic or exponential stability.Finally, a rotating arm that enters in contact with the external environment is studied in case the link is considered as being both rigid or flexible. Since this system exhibits instant changes in the impact times, we study this problem with the help of switching theory applied to infinite dimensional systems.L'objectif de cette thèse est de fournir un cadre mathématique permettant d'expliciter les modèles dynamiques d'une classe de mécanismes flexibles, de concevoir des lois de commandes adaptée et d'analyser le comportement asymptotique en boucle fermée qui en résulte. D'un point de vue mathématique, les parties flexibles sont décrites par des équations aux dérivée partielles (EDP), alors que la dynamique des parties rigides est décrite par des équations aux dérivée ordinaires (EDO). Par conséquent, le modèle global est décrit par un ensemble mixte de EDO-EDP (m-EDO-EDP), que en cette thèse est etudié en utilisant l'approche hamiltonienne à ports combinée à la théorie des semi-groupes.Tout d'abord, nous définissons une procédure rigoureuse basée sur le principe de moindre action afin d'établir le modèle des mécanismes avec d'éventuels composants flexibles, en fournissant plusieurs exemples illustratifs. Les parties à paramètres distribuées sont modélisées comme des systèmes de contrôle frontière unidimensionnels.Dans un second temps, différentes lois de commande stabilisantes sont synthétisées sur une classe de systèmes m-EDP-EDO linéaires. Les lois de commande proposées permettent d'atteindre une stabilité asymptotique ou exponentielle.Enfin, nous nous intéressons au problème de contact entre un bras rotatif et son environnement dans le cas où le système en rotation est considéré comme étant rigide ou flexible. Puisque ce système présente des changements instantanés dans les temps d'impact, nous étudions ce problème à l'aide de la théorie de commutation appliquée à des systèmes de dimensions infinie

Hybrid consensus for multi-agent systems with time-driven jumps

International audienceIn this paper, the behavior of scalar multi-agent systems over networks subject to time-driven jumps. Assuming that all agents communicate through distinct communication digraphs at jump and flow times, the asymptotic multi-consensus behavior of the hybrid network is explicitly characterized. The hybrid multi-consensus is shown to be associated with a suitable partition that is almost equitable for both the jump and flow communication digraphs. In doing so, no assumption on the underlying digraphs is introduced. Finally, the coupling rules making the multi-consensus subspace attractive are established. Several simulation examples illustrate the theoretical results

Infinite dimensional model of a double flexible-link manipulator: The Port-Hamiltonian approach

International audienceThis paper proposes a modular and control oriented model of a double flexible-link manipulator that stems from the modelling of a spatial flexible robot. The model consists of the power preserving interconnection between two infinite dimensional systems describing the beam’s motion and deformation with a finite dimensional nonlinear system describing the dynamics of the actuated rotating joints. To derive the model, Timoshenko’s assumptions are made for the flexible beams. Using Hamilton’s principle, the dynamic equations of the system are derived and then written in the Port-Hamiltonian (PH) framework through a proper choice of the state variables. These so called energy variables allow to write the total energy as a quadratic form with respect to a state dependent energy matrix. The resulting model is shown to be a passive system, a convenient property for control design purposes