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See detailCalcium signals driven by single channel noise.
Skupin, Alexander UL; Kettenmann, Helmut; Falcke, Martin

in PLoS computational biology (2010), 6(8),

Usually, the occurrence of random cell behavior is appointed to small copy numbers of molecules involved in the stochastic process. Recently, we demonstrated for a variety of cell types that intracellular ... [more ▼]

Usually, the occurrence of random cell behavior is appointed to small copy numbers of molecules involved in the stochastic process. Recently, we demonstrated for a variety of cell types that intracellular Ca2+ oscillations are sequences of random spikes despite the involvement of many molecules in spike generation. This randomness arises from the stochastic state transitions of individual Ca2+ release channels and does not average out due to the existence of steep concentration gradients. The system is hierarchical due to the structural levels channel--channel cluster--cell and a corresponding strength of coupling. Concentration gradients introduce microdomains which couple channels of a cluster strongly. But they couple clusters only weakly; too weak to establish deterministic behavior on cell level. Here, we present a multi-scale modelling concept for stochastic hierarchical systems. It simulates active molecules individually as Markov chains and their coupling by deterministic diffusion. Thus, we are able to follow the consequences of random single molecule state changes up to the signal on cell level. To demonstrate the potential of the method, we simulate a variety of experiments. Comparisons of simulated and experimental data of spontaneous oscillations in astrocytes emphasize the role of spatial concentration gradients in Ca2+ signalling. Analysis of extensive simulations indicates that frequency encoding described by the relation between average and standard deviation of interspike intervals is surprisingly robust. This robustness is a property of the random spiking mechanism and not a result of control. [less ▲]

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See detailCalcium transport in cardiovascular health and disease--the sarcolemmal calcium pump enters the stage.
Cartwright, Elizabeth J.; Schuh, Kai; Neyses, Ludwig UL

in Journal of Molecular and Cellular Cardiology (2005), 39(3), 403-6

Calcium is known to be one of the most important ionic regulators of the heart, where it has a crucial role in contraction-relaxation. Within a single beat of the cardiomyocyte there is a 100-fold ... [more ▼]

Calcium is known to be one of the most important ionic regulators of the heart, where it has a crucial role in contraction-relaxation. Within a single beat of the cardiomyocyte there is a 100-fold increase in the cytosolic free Ca(2+) level, this must be returned to its original concentration in order to maintain the normal physiological function of the cell. Two of the mechanisms involved in returning the Ca(2+) concentration back to resting levels are located at the sarcolemma; the sodium/calcium exchanger (NCX) and the sarcolemmal calcium pump. Compared to the NCX the sarcolemmal calcium pump extrudes significantly less calcium from the cardiomyocyte and has long been thought to be involved in the maintenance of low diastolic calcium levels. This review will outline recent evidence suggesting that the sarcolemmal calcium pump may in fact play a key role in signal transduction in the cardiovascular system. [less ▲]

Detailed reference viewed: 119 (1 UL)
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See detailCalcium transport systems in pressure overload cardiomyopathy
Neyses, Ludwig UL

in Timio, M; Wizemann, V; Venanzi, S (Eds.) Cardionephrology (1995)

Detailed reference viewed: 45 (0 UL)
See detailLe calcul mental à l'école élémentaire : Les bases du calcul nécessaires à l'apprentissage des mathématiques
Gamo, Sylvie UL; Djament, Daniel

Book published by Hachette - Hachette édication (2009)

Detailed reference viewed: 115 (3 UL)
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See detailLe Calcul Quantique
Bernard, Nicolas UL

Bachelor/master dissertation (2012)

Un ordinateur est un objet physique effectuant des opérations logiques, il a donc nécessairement besoin d’un substrat physique pour faire ces opérations. Aussi, si la théorie qui sous-tend l’informatique ... [more ▼]

Un ordinateur est un objet physique effectuant des opérations logiques, il a donc nécessairement besoin d’un substrat physique pour faire ces opérations. Aussi, si la théorie qui sous-tend l’informatique doit beaucoup aux mathématiciens (Turing pour n’en citer qu’un), c’est la physique qui a rendu la réalisation concrète des ordinateurs possible, qu’ils soient réalisés avec des relais électromécaniques, des tubes électroniques ou des transistors. Et cela ne s’arrête pas là : par exemple, d’une part la miniaturisation de ces derniers dans les processeurs fait que les phénomènes quantiques doivent être pris en compte (les électrons risquent de passer d’un fil à un autre par effet tunnel), d’autre part l’accroissement de la vitesse d’horloge rend concrète la barrière qu’est la vitesse de la lumière. Si les ordinateurs ne sont possibles qu’avec une théorie physique suffisamment évoluée, il y a une rétroaction qui se crée, car la physique a beaucoup bénéficié du développement des ordinateurs. Ceux-ci rendent en effet possibles des calculs – d’abord numériques, mais également symboliques – qu’il serait difficile de faire « à la main », pour des questions de temps et « d’erreurs humaines ». Cette possibilité a ouvert la voie à des simulations dans pratiquement toutes les branches de la physique, et ces simulations ont à leur tour pratique- ment créé de nouvelles branches, telle la théorie du chaos. En 1982, Richard Feynman déplorait cependant que les simulations informatiques de processus quantiques ne fussent pas efficaces, et suggérait qu’elles pourraient être bien plus rapides si l’ordinateur était lui-même « quantique » [2]. Dans ce document, nous allons d’abord revenir (chapitre 1) sur ce point et expliquer ce que pourrait faire différemment un ordinateur « quantique ». Nous décrirons ensuite (chapitre 2) les bases théoriques du calcul quantique tel que pourrait le pratiquer un ordinateur de ce type. Nous verrons finalement (chapitre 3) avec l’exemple de l’algorithme de Shor et de la Tranformation de Fourier Quantique qu’au-delà des simulations de processus quantiques, un ordinateur quantique pourrait accélérer dramatiquement d’autres opérations. Nous conclurons sur quelques approches possibles pour la réalisation d’un ordinateur quantique et sur l’existence d’autres applications de la mécanique quantique liées à l’informatique et à la communication qui ne nécessitent pas forcément un tel ordinateur, ainsi que sur des aspects plus philosophiques du calcul quantique. [less ▲]

Detailed reference viewed: 185 (19 UL)
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See detailLe calcul stochastique
Schiltz, Jang UL

Presentation (2000, May 17)

Detailed reference viewed: 24 (0 UL)
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See detailCalculating the Malliavin derivative of some stochastic mechanics problems
Hauseux, Paul UL; Hale, Jack UL; Bordas, Stéphane UL

in PLoS ONE (2017), 12(12), 0189994

The Malliavin calculus is an extension of the classical calculus of variations from deterministic functions to stochastic processes. In this paper we aim to show in a practical and didactic way how to ... [more ▼]

The Malliavin calculus is an extension of the classical calculus of variations from deterministic functions to stochastic processes. In this paper we aim to show in a practical and didactic way how to calculate the Malliavin derivative, the derivative of the expectation of a quantity of interest of a model with respect to its underlying stochastic parameters, for four problems found in mechanics. The non-intrusive approach uses the Malliavin Weight Sampling (MWS) method in conjunction with a standard Monte Carlo method. The models are expressed as ODEs or PDEs and discretised using the finite difference or finite element methods. Specifically, we consider stochastic extensions of; a 1D Kelvin-Voigt viscoelastic model discretised with finite differences, a 1D linear elastic bar, a hyperelastic bar undergoing buckling, and incompressible Navier-Stokes flow around a cylinder, all discretised with finite elements. A further contribution of this paper is an extension of the MWS method to the more difficult case of non-Gaussian random variables and the calculation of second-order derivatives. We provide open-source code for the numerical examples in this paper. [less ▲]

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See detailCalculs de paramètres RMN de fluorures inorganiques cristallisés
Bernard, Nicolas UL

Bachelor/master dissertation (2015)

The goal of this work was to compute the NMR parameters of some crystalline inorganic fluorides using the Gipaw method as implemented in Quantum-Espresso. Notably, we were interested in reproducing (or ... [more ▼]

The goal of this work was to compute the NMR parameters of some crystalline inorganic fluorides using the Gipaw method as implemented in Quantum-Espresso. Notably, we were interested in reproducing (or not) some published results [16, 17] that had been obtained using Castep. [less ▲]

Detailed reference viewed: 99 (13 UL)
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See detailCALCURIX: a "tailor-made" RM software
Schiltz, Jang UL; Fadiga, Isamel

Presentation (2017, March 15)

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See detailA Calibrated Learning Approach to Distributed Power Allocation in Small Cell Networks
Zhang, Xinruo; Nakhai; Zheng, Gan UL et al

in ICASSP 2019 - 2019 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP) (2019, April 17)

This paper studies the problem of max-min fairness power allocation in distributed small cell networks operated under the same frequency bandwidth. We introduce a calibrated learning enhanced time ... [more ▼]

This paper studies the problem of max-min fairness power allocation in distributed small cell networks operated under the same frequency bandwidth. We introduce a calibrated learning enhanced time division multiple access scheme to optimize the transmit power decisions at the small base stations (SBSs) and achieve max-min user fairness in the long run. Provided that the SBSs are autonomous decision makers, the aim of the proposed algorithm is to allow SBSs to gradually improve their forecast of the possible transmit power levels of the other SBSs and react with the best response based on the predicted results at individual time slots. Simulation results validate that in terms of achieving max-min signal-to-interference-plus-noise ratio, the proposed distributed design outperforms two benchmark schemes and achieves a similar performance as compared to the optimal centralized design. [less ▲]

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See detailCalibrated Learning for Online Distributed Power Allocation in Small-Cell Networks
Zhang, Xinruo; Nakhai, Mohammad Reza; Zheng, Gan UL et al

in IEEE Transactions on Communications (2019), 67(11), 8124-8136

This paper introduces a combined calibrated learning and bandit approach to online distributed power control in small cell networks operated under the same frequency bandwidth. Each small base station ... [more ▼]

This paper introduces a combined calibrated learning and bandit approach to online distributed power control in small cell networks operated under the same frequency bandwidth. Each small base station (SBS) is modelled as an intelligent agent who autonomously decides on its instantaneous transmit power level by predicting the transmitting policies of the other SBSs, namely the opponent SBSs, in the network, in real-time. The decision making process is based jointly on the past observations and the calibrated forecasts of the upcoming power allocation decisions of the opponent SBSs who inflict the dominant interferences on the agent. Furthermore, we integrate the proposed calibrated forecast process with a bandit policy to account for the wireless channel conditions unknown a priori , and develop an autonomous power allocation algorithm that is executable at individual SBSs to enhance the accuracy of the autonomous decision making. We evaluate the performance of the proposed algorithm in cases of maximizing the long-term sum-rate, the overall energy efficiency and the average minimum achievable data rate. Numerical simulation results demonstrate that the proposed design outperforms the benchmark scheme with limited amount of information exchange and rapidly approaches towards the optimal centralized solution for all case studies. [less ▲]

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See detailCalibration of a microscopic simulation model for emission calculation
Li, Jie; Van Zuylen, Henk J.; Chen, Yusen et al

in Transportation Research. Part C : Emerging Technologies (2013), 31

Emissions by road traffic can be reduced by optimising traffic control. The impact of this optimisation on emission can be analysed ex ante by simulation. The simulation programs used for this analysis ... [more ▼]

Emissions by road traffic can be reduced by optimising traffic control. The impact of this optimisation on emission can be analysed ex ante by simulation. The simulation programs used for this analysis should be valid with respect to the traffic characteristics that determine the emissions. Thus calibration of the parameters is a prerequisite. In most cases, volumes, travel times and queues are used to calibrate simulation models, rather than detailed driving characteristics such as speed and acceleration patterns. However, these driving behaviour parameters determine the vehicular emissions to a great extent. A study was carried out in which the driving behaviour parameters in a microscopic simulation model (VISSIM) were calibrated using real trajectories collected by image processing at an intersection in Rotterdam. The sensitivity of the simulation results for driving behaviour parameters was investigated. The most influential parameters were identified and adjusted to ensure that the simulation results were consistent with the observed traffic and could provide valid estimations of the total production of emissions. [less ▲]

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See detailCalibration of a superconducting gravimeter by comparison with an absolute gravimeter FG5 in Boulder
Francis, Olivier UL; Niebauer, T. M.; Sasagawa, G. et al

in Geophysical Research Letters (1998), 25(7), 1075-1078

Detailed reference viewed: 116 (2 UL)
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See detailCalibration of households preference for open-spaces from an urban cellular automata model: method and application to Dijon
Caruso, Geoffrey UL; Hilal, Mohamed

in Foltête, Jean-Christophe (Ed.) Actes des Huitièmes Rencontres de Théo Quant (2008)

We propose a calibration method for a residential growth model that is grounded on a microeconomic cellular automaton. This model can be seen as a spatial and dynamic representation of an urban economic ... [more ▼]

We propose a calibration method for a residential growth model that is grounded on a microeconomic cellular automaton. This model can be seen as a spatial and dynamic representation of an urban economic model with neighbourhood externalities. A 2D spatial equilibrium of residential locations is obtained stepwise through time instead of being a one-shot instantaneous equilibrium. Previous research work showed that the model can produce more or less dense and fragmented urban patterns depending on the preference of households for open space. We propose here a method for calibrating those preferences from simulations of the model and land rents observed within the Dijon urban area. More precisely, equilibrium properties of the model are used to derive the elasticity of open-space preferences. Then simulations are used to estimate the neighbourhood distance to which open-space are valued by households. Our first results tend to support our residential behaviour assumptions and tend to be in accordance with results obtained with more classic methods. Further methodological improvements are however needed. [less ▲]

Detailed reference viewed: 62 (3 UL)
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See detailCalibration of normalised CES production functions in dynamic models
Klump, Rainer UL; Saam, Marianne

in ECONOMICS LETTERS (2008), 99(2), 256-259

Normalising CES production functions allows to choose technology parameters of dynamic models in a plausible way and excludes arbitrary effects of changes in the elasticity of substitution. As an ... [more ▼]

Normalising CES production functions allows to choose technology parameters of dynamic models in a plausible way and excludes arbitrary effects of changes in the elasticity of substitution. As an illustration, the speed of convergence in the Ramsey model is considered. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailCalibration of the C021 superconducting gravimeter in Membach (Belgium) using 47 days of absolute gravity measurements
Francis, Olivier UL

in Segawa, Jiro; Fujimoto, Hiromi; Okubo, Shubei (Eds.) Gravity, Geoid and Marine Geodesy (1997)

Detailed reference viewed: 150 (5 UL)
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See detailCalibration of the LaCoste-Romberg 906 by Comparison with the Superconducting Gavimeter C021 in Membach (Belgium)
Francis, Olivier UL; Hendrickx, Marc

in Journal of the Geodetic Society of Japan (2001), 47(1), 16-21

Detailed reference viewed: 87 (4 UL)
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See detailCalibration of the Tide Gauge at King Edward Point, South Georgia Island
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Woodworth, P L et al

Poster (2015, March 12)

After initial sea level observations in the 1950s, a new pressure tide gauge (Global Sea Level Observing System 187) was installed at King Edward Point (KEP), South Georgia Island, British Overseas ... [more ▼]

After initial sea level observations in the 1950s, a new pressure tide gauge (Global Sea Level Observing System 187) was installed at King Edward Point (KEP), South Georgia Island, British Overseas Territories in the South Atlantic Ocean, in 2008. This was car-ried out as part of the ACCLAIM (Antarctic Circumpolar Current Levels by Altimetry and Island Measurements) programme. In 2013 the KEP Geodetic Observato-ry was established in support of various geoscience applications including the monitor-ing of vertical land movements at KEP. Currently, the observatory consists of two state-of-the-art GNSS stations with local benchmark networks, allowing the height determina-tions from the GNSS antennas to be transferred to the tide gauge and forming a height reference within the International Terrestrial Reference Frame. Finally in 2014, a tide board was added to the tide gauge, which, together with the GNSS and levelling obser-vations, now allows the calibration of the tide gauge. In this study, we will present the results from the calibration of the tide gauge using the GNSS observations from the KEP Geodetic Observatory for the period from February 2013 to present, the levelling campaigns in 2013 and 2014, and geoid undulations de-rived from a seamless combination of the latest GOCO and EGM2008 gravity models. [less ▲]

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See detailCalibration of the Tide Gauge at King Edward Point, South Georgia Island, South Atlantic Ocean
Teferle, Felix Norman UL; Hunegnaw, Addisu UL; Woodworth, P. L. et al

Poster (2015, June 27)

In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried out ... [more ▼]

In 2008 a new pressure tide gauge with Global Sea Level Observing System Number 187 was installed at King Edward Point (KEP), South Georgia Island, South Atlantic Ocean. This installation was carried out as part of the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements (ACCLAIM) programme. In 2013 the KEP Geodetic Observatory was established in support of various scientific applications including the monitoring of vertical land movements at KEP. Currently, the observatory consists of two state-of-the-art Global Navigation Satellite System (GNSS) stations with local benchmark networks. This ties all benchmarks and the tide gauge into the International Terrestrial Reference Frame 2008, and allows the establishment of a local height datum in a global height system through the use of a global gravitational model. In 2014 a tide board was added to the tide gauge, which, together with the GNSS and levelling observations, now enables a calibration of the tide gauge. This will make it possible to include the KEP tide gauge in the Permanent Service for Mean Sea Level (PSMSL) database. In this study, we will present the results from the calibration of the tide gauge using the GNSS observations from the KEP Geodetic Observatory for the period from February 2013 to present, the levelling campaigns in 2013 and 2014, and geoid undulations derived from a seamless combination of the latest Gravity Observation Combination (GOCO) 05S and Earth Gravitational Model (EGM) 2008 models. [less ▲]

Detailed reference viewed: 111 (6 UL)