The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Ramon Costa-castelló - One of the best experts on this subject based on the ideXlab platform.

  • Model-based analysis for the thermal management of open-cathode proton exchange membrane fuel cell systems concerning efficiency and stability
    Journal of Process Control, 2016
    Co-Authors: Stephan Strahl, Ramon Costa-castelló
    Abstract:

    In this work we present a dynamic, control-oriented, concentrated parameter model of an open-cathode proton exchange membrane fuel cell system for the study of stability and efficiency improvement with respect to thermal management. The system model consists of two dynamic States which are the fuel cell temperature and the liquid water saturation in the cathode catalyst layer. The control action of the system is the inlet air velocity of the cathode air flow manifold, set by the cooling fan, and the system output is the stack voltage. From the model we derive the equilibrium points and eigenvalues within a set of operating conditions and subsequently discuss stability and the possibility of efficiency improvement. The model confirms the existence of a temperature-dependent maximum power in the moderate temperature region. The stability analysis shows that the maximum power line decomposes the phase plane in two parts, namely Stable and unStable equilibrium points. The model is capable of predicting the temperature of a Stable Steady-State voltage maximum and the simulation results serve for the design of optimal thermal management strategies.

Christoph Walker - One of the best experts on this subject based on the ideXlab platform.

  • A Parabolic Free Boundary Problem Modeling Electrostatic MEMS
    Archive for Rational Mechanics and Analysis, 2014
    Co-Authors: Joachim Escher, Philippe Laurençot, Christoph Walker
    Abstract:

    The evolution problem for a membrane based model of an electrostatically actuated microelectromechanical system is studied. The model describes the dynamics of the membrane displacement and the electric potential. The latter is a harmonic function in an angular domain, the deformable membrane being a part of the boundary. The former solves a heat equation with a right-hand side that depends on the square of the trace of the gradient of the electric potential on the membrane. The resulting free boundary problem is shown to be well-posed locally in time. Furthermore, solutions corresponding to small voltage values exist globally in time, while global existence is shown not to hold for high voltage values. It is also proven that, for small voltage values, there is an asymptotically Stable Steady-State solution. Finally, the small aspect ratio limit is rigorously justified.

  • a parabolic free boundary problem modeling electrostatic mems
    arXiv: Analysis of PDEs, 2012
    Co-Authors: Joachim Escher, Philippe Laurençot, Christoph Walker
    Abstract:

    The evolution problem for a membrane based model of an electrostatically actuated microelectromechanical system (MEMS) is studied. The model describes the dynamics of the membrane displacement and the electric potential. The latter is a harmonic function in an angular domain, the deformable membrane being a part of the boundary. The former solves a heat equation with a right hand side that depends on the square of the trace of the gradient of the electric potential on the membrane. The resulting free boundary problem is shown to be well-posed locally in time. Furthermore, solutions corresponding to small voltage values exist globally in time while global existence is shown not to hold for high voltage values. It is also proven that, for small voltage values, there is an asymptotically Stable Steady-State solution. Finally, the small aspect ratio limit is rigorously justified.

Stephan Strahl - One of the best experts on this subject based on the ideXlab platform.

  • Model-based analysis for the thermal management of open-cathode proton exchange membrane fuel cell systems concerning efficiency and stability
    Journal of Process Control, 2016
    Co-Authors: Stephan Strahl, Ramon Costa-castelló
    Abstract:

    In this work we present a dynamic, control-oriented, concentrated parameter model of an open-cathode proton exchange membrane fuel cell system for the study of stability and efficiency improvement with respect to thermal management. The system model consists of two dynamic States which are the fuel cell temperature and the liquid water saturation in the cathode catalyst layer. The control action of the system is the inlet air velocity of the cathode air flow manifold, set by the cooling fan, and the system output is the stack voltage. From the model we derive the equilibrium points and eigenvalues within a set of operating conditions and subsequently discuss stability and the possibility of efficiency improvement. The model confirms the existence of a temperature-dependent maximum power in the moderate temperature region. The stability analysis shows that the maximum power line decomposes the phase plane in two parts, namely Stable and unStable equilibrium points. The model is capable of predicting the temperature of a Stable Steady-State voltage maximum and the simulation results serve for the design of optimal thermal management strategies.

Albert Goldbeter - One of the best experts on this subject based on the ideXlab platform.

  • a skeleton model for the network of cyclin dependent kinases driving the mammalian cell cycle
    Interface Focus, 2011
    Co-Authors: Claude Gerard, Albert Goldbeter
    Abstract:

    We previously proposed a detailed, 39-variable model for the network of cyclin-dependent kinases (Cdks) that controls progression along the successive phases of the mammalian cell cycle. Here, we propose a skeleton, 5-variable model for the Cdk network that can be seen as the backbone of the more detailed model for the mammalian cell cycle. In the presence of sufficient amounts of growth factor, the skeleton model also passes from a Stable Steady State to sustained oscillations of the various cyclin/Cdk complexes. This transition corresponds to the switch from quiescence to cell proliferation. Sequential activation of the cyclin/Cdk complexes allows the ordered progression along the G1, S, G2 and M phases of the cell cycle. The 5-variable model can also account for the existence of a restriction point in G1, and for endoreplication. Like the detailed model, it contains multiple oscillatory circuits and can display complex oscillatory behaviour such as quasi-periodic oscillations and chaos. We compare the dynamical properties of the skeleton model with those of the more detailed model for the mammalian cell cycle.

  • temporal self organization of the cyclin cdk network driving the mammalian cell cycle
    Proceedings of the National Academy of Sciences of the United States of America, 2009
    Co-Authors: Claude Gerard, Albert Goldbeter
    Abstract:

    We propose an integrated computational model for the network of cyclin-dependent kinases (Cdks) that controls the dynamics of the mammalian cell cycle. The model contains four Cdk modules regulated by reversible phosphorylation, Cdk inhibitors, and protein synthesis or degradation. Growth factors (GFs) trigger the transition from a quiescent, Stable Steady State to self-sustained oscillations in the Cdk network. These oscillations correspond to the repetitive, transient activation of cyclin D/Cdk4–6 in G1, cyclin E/Cdk2 at the G1/S transition, cyclin A/Cdk2 in S and at the S/G2 transition, and cyclin B/Cdk1 at the G2/M transition. The model accounts for the following major properties of the mammalian cell cycle: (i) repetitive cell cycling in the presence of suprathreshold amounts of GF; (ii) control of cell-cycle progression by the balance between antagonistic effects of the tumor suppressor retinoblastoma protein (pRB) and the transcription factor E2F; and (iii) existence of a restriction point in G1, beyond which completion of the cell cycle becomes independent of GF. The model also accounts for endoreplication. Incorporating the DNA replication checkpoint mediated by kinases ATR and Chk1 slows down the dynamics of the cell cycle without altering its oscillatory nature and leads to better separation of the S and M phases. The model for the mammalian cell cycle shows how the regulatory structure of the Cdk network results in its temporal self-organization, leading to the repetitive, sequential activation of the four Cdk modules that brings about the orderly progression along cell-cycle phases.

  • from simple to complex oscillatory behavior in metabolic and genetic control networks
    Chaos, 2001
    Co-Authors: Albert Goldbeter, Didier Gonze, Gerald Houart, Jeanchristophe Leloup, Jose Halloy, Genevieve Dupont
    Abstract:

    We present an overview of mechanisms responsible for simple or complex oscillatory behavior in metabolic and genetic control networks. Besides simple periodic behavior corresponding to the evolution toward a limit cycle we consider complex modes of oscillatory behavior such as complex periodic oscillations of the bursting type and chaos. Multiple attractors are also discussed, e.g., the coexistence between a Stable Steady State and a Stable limit cycle (hard excitation), or the coexistence between two simultaneously Stable limit cycles (birhythmicity). We discuss mechanisms responsible for the transition from simple to complex oscillatory behavior by means of a number of models serving as selected examples. The models were originally proposed to account for simple periodic oscillations observed experimentally at the cellular level in a variety of biological systems. In a second stage, these models were modified to allow for complex oscillatory phenomena such as bursting, birhythmicity, or chaos. We consid...

Joachim Escher - One of the best experts on this subject based on the ideXlab platform.

  • A Parabolic Free Boundary Problem Modeling Electrostatic MEMS
    Archive for Rational Mechanics and Analysis, 2014
    Co-Authors: Joachim Escher, Philippe Laurençot, Christoph Walker
    Abstract:

    The evolution problem for a membrane based model of an electrostatically actuated microelectromechanical system is studied. The model describes the dynamics of the membrane displacement and the electric potential. The latter is a harmonic function in an angular domain, the deformable membrane being a part of the boundary. The former solves a heat equation with a right-hand side that depends on the square of the trace of the gradient of the electric potential on the membrane. The resulting free boundary problem is shown to be well-posed locally in time. Furthermore, solutions corresponding to small voltage values exist globally in time, while global existence is shown not to hold for high voltage values. It is also proven that, for small voltage values, there is an asymptotically Stable Steady-State solution. Finally, the small aspect ratio limit is rigorously justified.

  • a parabolic free boundary problem modeling electrostatic mems
    arXiv: Analysis of PDEs, 2012
    Co-Authors: Joachim Escher, Philippe Laurençot, Christoph Walker
    Abstract:

    The evolution problem for a membrane based model of an electrostatically actuated microelectromechanical system (MEMS) is studied. The model describes the dynamics of the membrane displacement and the electric potential. The latter is a harmonic function in an angular domain, the deformable membrane being a part of the boundary. The former solves a heat equation with a right hand side that depends on the square of the trace of the gradient of the electric potential on the membrane. The resulting free boundary problem is shown to be well-posed locally in time. Furthermore, solutions corresponding to small voltage values exist globally in time while global existence is shown not to hold for high voltage values. It is also proven that, for small voltage values, there is an asymptotically Stable Steady-State solution. Finally, the small aspect ratio limit is rigorously justified.