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Статті в журналах з теми "Equilibrage des charge"
1
Weber, S. L. "A timescale analysis of the NH temperature response to volcanic and solar forcing in the past millenium." Climate of the Past Discussions 1, no. 2 (September 8, 2005): 137–53. http://dx.doi.org/10.5194/cpd-1-137-2005.
Повний текст джерелаАнотація:
Abstract. The Northern Hemisphere temperature response to volcanic and solar forcing is studied using first a set of simulations with an intermediate-complexity climate model, driven by reconstructed forcings. Results are than compared with those obtained from the seven high-resolution reconstructed temperature records for the last millenium that are at present available. Focus of the analysis is on the timescale dependence of the response. Results between the model and the proxy-based reconstructions are remarkably consistent. The response to solar forcing is found to equilibrate at interdecadal timescales, reaching an equilibrium value for the regression of 0.2-0.3°C per W/m2. The time interval between volcanic eruptions is typically shorter than the dissipation timescale of the climate system, so that the response to volcanic forcing never equilibrates. As a result, the regression on the volcanic forcing is always lower than the equilibrium value and goes to zero for the longest temporal scales. The trends over the pre-anthropogenic period are found to be relatively large in all reconstructed temperature records compared to their interdecadal-centennial variability. This is at variance with a recent claim that reconstructed temperature records underestimate climatic variations at multi-centennial scales.
2
Weber, S. L. "A timescale analysis of the Northern Hemisphere temperature response to volcanic and solar forcing." Climate of the Past 1, no. 1 (December 5, 2005): 9–17. http://dx.doi.org/10.5194/cp-1-9-2005.
Повний текст джерелаАнотація:
Abstract. The Northern Hemisphere temperature response to volcanic and solar forcing in the time interval 1000–1850 AD is studied using first a set of simulations with an intermediate-complexity climate model, driven by reconstructed forcings. Results are then compared with those obtained from the seven high-resolution reconstructed temperature records for the last millenium that are at present available. Focus of the analysis is on the timescale dependence of the response. Results between the model and the proxy-based reconstructions are remarkably consistent. The response to solar forcing is found to equilibrate at interdecadal timescales, reaching an equilibrium value for the regression of 0.2–0.3°C per W/m2. The time interval between volcanic eruptions is typically shorter than the dissipation timescale of the climate system, so that the response to volcanic forcing never equilibrates. As a result, the regression on the volcanic forcing is always lower than the equilibrium value and goes to zero for the longest temporal scales. The trends over the pre-anthropogenic period are found to be relatively large in all reconstructed temperature records, given the trends in the reconstructed forcing and the equilibrium value for the regression. This is at variance with a recent claim that reconstructed temperature records underestimate climatic variations at multi-centennial timescales.
3
Yutkin, Maxim P., Himanshu Mishra, Tadeusz W. Patzek, John Lee, and Clayton J. Radke. "Bulk and Surface Aqueous Speciation of Calcite: Implications for Low-Salinity Waterflooding of Carbonate Reservoirs." SPE Journal 23, no. 01 (August 25, 2017): 84–101. http://dx.doi.org/10.2118/182829-pa.
Повний текст джерелаАнотація:
Summary Low-salinity waterflooding (LSW) is ineffective when reservoir rock is strongly water-wet or when crude oil is not asphaltenic. Success of LSW relies heavily on the ability of injected brine to alter surface chemistry of reservoir crude-oil brine/rock (COBR) interfaces. Implementation of LSW in carbonate reservoirs is especially challenging because of high reservoir-brine salinity and, more importantly, because of high reactivity of the rock minerals. Both features complicate understanding of the COBR surface chemistries pertinent to successful LSW. Here, we tackle the complex physicochemical processes in chemically active carbonates flooded with diluted brine that is saturated with atmospheric carbon dioxide (CO2) and possibly supplemented with additional ionic species, such as sulfates or phosphates. When waterflooding carbonate reservoirs, rock equilibrates with the injected brine over short distances. Injected-brine ion speciation is shifted substantially in the presence of reactive carbonate rock. Our new calculations demonstrate that rock-equilibrated aqueous pH is slightly alkaline quite independent of injected-brine pH. We establish, for the first time, that CO2 content of a carbonate reservoir, originating from CO2-rich crude oil and gas, plays a dominant role in setting aqueous pH and rock-surface speciation. A simple ion-complexing model predicts the calcite-surface charge as a function of composition of reservoir brine. The surface charge of calcite may be positive or negative, depending on speciation of reservoir brine in contact with the calcite. There is no single point of zero charge; all dissolved aqueous species are charge determining. Rock-equilibrated aqueous composition controls the calcite-surface ion-exchange behavior, not the injected-brine composition. At high ionic strength, the electrical double layer collapses and is no longer diffuse. All surface charges are located directly in the inner and outer Helmholtz planes. Our evaluation of calcite bulk and surface equilibria draws several important inferences about the proposed LSW oil-recovery mechanisms. Diffuse double-layer expansion (DLE) is impossible for brine ionic strength greater than 0.1 molar. Because of rapid rock/brine equilibration, the dissolution mechanism for releasing adhered oil is eliminated. Also, fines mobilization and concomitant oil release cannot occur because there are few loose fines and clays in a majority of carbonates. LSW cannot be a low-interfacial-tension alkaline flood because carbonate dissolution exhausts all injected base near the wellbore and lowers pH to that set by the rock and by formation CO2. In spite of diffuse double-layer collapse in carbonate reservoirs, surface ion-exchange oil release remains feasible, but unproved.
4
D'Avanzo, Nazzareno, Hee Cheol Cho, Illya Tolokh, Roman Pekhletski, Igor Tolokh, Chris Gray, Saul Goldman, and Peter H. Backx. "Conduction through the Inward Rectifier Potassium Channel, Kir2.1, Is Increased by Negatively Charged Extracellular Residues." Journal of General Physiology 125, no. 5 (April 11, 2005): 493–503. http://dx.doi.org/10.1085/jgp.200409175.
Повний текст джерелаАнотація:
Ion channel conductance can be influenced by electrostatic effects originating from fixed “surface” charges that are remote from the selectivity filter. To explore whether surface charges contribute to the conductance properties of Kir2.1 channels, unitary conductance was measured in cell-attached recordings of Chinese hamster ovary (CHO) cells transfected with Kir2.1 channels over a range of K+ activities (4.6–293.5 mM) using single-channel measurements as well as nonstationary fluctuation analysis for low K+ activities. K+ ion concentrations were shown to equilibrate across the cell membrane in our studies using the voltage-sensitive dye DiBAC4(5). The dependence of γ on the K+ activity (aK) was fit well by a modified Langmuir binding isotherm, with a nonzero intercept as aK approaches 0 mM, suggesting electrostatic surface charge effects. Following the addition of 100 mM N-methyl-d-glucamine (NMG+), a nonpermeant, nonblocking cation or following pretreatment with 50 mM trimethyloxonium (TMO), a carboxylic acid esterifying agent, the γ–aK relationship did not show nonzero intercepts, suggesting the presence of surface charges formed by glutamate or aspartate residues. Consistent with surface charges in Kir2.1 channels, the rates of current decay induced by Ba2+ block were slowed with the addition of NMG or TMO. Using a molecular model of Kir2.1 channels, three candidate negatively charged residues were identified near the extracellular mouth of the pore and mutated to cysteine (E125C, D152C, and E153C). E153C channels, but not E125C or D152C channels, showed hyperbolic γ–aK relationships going through the origin. Moreover, the addition of MTSES to restore the negative charges in E53C channels reestablished wild-type conductance properties. Our results demonstrate that E153 contributes to the conductance properties of Kir2.1 channels by acting as a surface charge.
5
Munday, David R., Helen L. Johnson, and David P. Marshall. "Eddy Saturation of Equilibrated Circumpolar Currents." Journal of Physical Oceanography 43, no. 3 (March 1, 2013): 507–32. http://dx.doi.org/10.1175/jpo-d-12-095.1.
Повний текст джерелаАнотація:
Abstract This study uses a sector configuration of an ocean general circulation model to examine the sensitivity of circumpolar transport and meridional overturning to changes in Southern Ocean wind stress and global diapycnal mixing. At eddy-permitting, and finer, resolution, the sensitivity of circumpolar transport to forcing magnitude is drastically reduced. At sufficiently high resolution, there is little or no sensitivity of circumpolar transport to wind stress, even in the limit of no wind. In contrast, the meridional overturning circulation continues to vary with Southern Ocean wind stress, but with reduced sensitivity in the limit of high wind stress. Both the circumpolar transport and meridional overturning continue to vary with diapycnal diffusivity at all model resolutions. The circumpolar transport becomes less sensitive to changes in diapycnal diffusivity at higher resolution, although sensitivity always remains. In contrast, the overturning circulation is more sensitive to change in diapycnal diffusivity when the resolution is high enough to permit mesoscale eddies.
6
Sentman, Lori T., Elena Shevliakova, Ronald J. Stouffer, and Sergey Malyshev. "Time Scales of Terrestrial Carbon Response Related to Land-Use Application: Implications for Initializing an Earth System Model." Earth Interactions 15, no. 30 (October 1, 2011): 1–16. http://dx.doi.org/10.1175/2011ei401.1.
Повний текст джерелаАнотація:
Abstract The dynamic vegetation and carbon cycling component, LM3V, of the Geophysical Fluid Dynamics Laboratory (GFDL) prototype Earth system model (ESM2.1), has been designed to simulate the effects of land use on terrestrial carbon pools, including secondary vegetation regrowth. Because of the long time scales associated with the carbon adjustment, special consideration is required when initializing the ESM when historical simulations are conducted. Starting from an equilibrated, preindustrial climate and potential vegetation state in an offline land-only model (LM3V), estimates of historical land use are instantaneously applied in five experiments beginning in the following calendar years: 1500, 1600, 1700, 1750, and 1800. This application results in the land carbon pools experiencing an abrupt change—a carbon shock—and the secondary vegetation needs time to regrow into consistency with the harvesting history. The authors find that it takes approximately 100 years for the vegetation to recover from the carbon shock, whereas soils take at least 150 years to recover. The vegetation carbon response is driven primarily by land-use history, whereas the soil carbon response is affected by both land-use history and the geographic pattern of soil respiration rates. Based on these results, the authors recommend the application of historical land-use scenarios in 1700 to provide sufficient time for the land carbon in ESMs with secondary vegetation to equilibrate to adequately simulate carbon stores at the start of the historical integrations (i.e., 1860) in a computationally efficient manner.
7
Messias, Andresa, Denys E. S. Santos, Frederico J. S. Pontes, Filipe S. Lima, and Thereza A. Soares. "Out of Sight, Out of Mind: The Effect of the Equilibration Protocol on the Structural Ensembles of Charged Glycolipid Bilayers." Molecules 25, no. 21 (November 4, 2020): 5120. http://dx.doi.org/10.3390/molecules25215120.
Повний текст джерелаАнотація:
Molecular dynamics (MD) simulations represent an essential tool in the toolbox of modern chemistry, enabling the prediction of experimental observables for a variety of chemical systems and processes and majorly impacting the study of biological membranes. However, the chemical diversity of complex lipids beyond phospholipids brings new challenges to well-established protocols used in MD simulations of soft matter and requires continuous assessment to ensure simulation reproducibility and minimize unphysical behavior. Lipopolysaccharides (LPS) are highly charged glycolipids whose aggregation in a lamellar arrangement requires the binding of numerous cations to oppositely charged groups deep inside the membrane. The delicate balance between the fully hydrated carbohydrate region and the smaller hydrophobic core makes LPS membranes very sensitive to the choice of equilibration protocol. In this work, we show that the protocol successfully used to equilibrate phospholipid bilayers when applied to complex lipopolysaccharide membranes occasionally leads to a small expansion of the simulation box very early in the equilibration phase. Although the use of a barostat algorithm controls the system dimension and particle distances according to the target pressure, fluctuation in the fleeting pressure occasionally enables a few water molecules to trickle into the hydrophobic region of the membrane, with spurious solvent buildup. We show that this effect stems from the initial steps of NPT equilibration, where initial pressure can be fairly high. This can be solved with the use of a stepwise-thermalization NVT/NPT protocol, as demonstrated for atomistic MD simulations of LPS/DPPE and lipid-A membranes in the presence of different salts using an extension of the GROMOS forcefield within the GROMACS software. This equilibration protocol should be standard procedure for the generation of consistent structural ensembles of charged glycolipids starting from atomic coordinates not previously pre-equilibrated. Although different ways to deal with this issue can be envisioned, we investigated one alternative that could be readily available in major MD engines with general users in mind.
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Roland, Steffen, Juliane Kniepert, John A. Love, Vikas Negi, Feilong Liu, Peter Bobbert, Armantas Melianas, Martijn Kemerink, Andreas Hofacker, and Dieter Neher. "Equilibrated Charge Carrier Populations Govern Steady-State Nongeminate Recombination in Disordered Organic Solar Cells." Journal of Physical Chemistry Letters 10, no. 6 (March 4, 2019): 1374–81. http://dx.doi.org/10.1021/acs.jpclett.9b00516.
Повний текст джерела
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Van Breedam, Jonas, Heiko Goelzer, and Philippe Huybrechts. "Semi-equilibrated global sea-level change projections for the next 10 000 years." Earth System Dynamics 11, no. 4 (November 6, 2020): 953–76. http://dx.doi.org/10.5194/esd-11-953-2020.
Повний текст джерелаАнотація:
Abstract. The emphasis for informing policy makers on future sea-level rise has been on projections by the end of the 21st century. However, due to the long lifetime of atmospheric CO2, the thermal inertia of the climate system and the slow equilibration of the ice sheets, global sea level will continue to rise on a multi-millennial timescale even when anthropogenic CO2 emissions cease completely during the coming decades to centuries. Here we present global sea-level change projections due to the melting of land ice combined with steric sea effects during the next 10 000 years calculated in a fully interactive way with the Earth system model of intermediate complexity LOVECLIMv1.3. The greenhouse forcing is based on the Extended Concentration Pathways defined until 2300 CE with no carbon dioxide emissions thereafter, equivalent to a cumulative CO2 release of between 460 and 5300 GtC. We performed one additional experiment for the highest-forcing scenario with the inclusion of a methane emission feedback where methane is slowly released due to a strong increase in surface and oceanic temperatures. After 10 000 years, the sea-level change rate drops below 0.05 m per century and a semi-equilibrated state is reached. The Greenland ice sheet is found to nearly disappear for all forcing scenarios. The Antarctic ice sheet contributes only about 1.6 m to sea level for the lowest forcing scenario with a limited retreat of the grounding line in West Antarctica. For the higher-forcing scenarios, the marine basins of the East Antarctic Ice Sheet also become ice free, resulting in a sea-level rise of up to 27 m. The global mean sea-level change after 10 000 years ranges from 9.2 to more than 37 m. For the highest-forcing scenario, the model uncertainty does not exclude the complete melting of the Antarctic ice sheet during the next 10 000 years.
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Cardoso, Eveline Coelho, and Glayci Kelli Reis da S. Xavier. "Tempo e narrativa no gênero charge: condensar para potencializar." Veredas: Revista da Associação Internacional de Lusitanistas, no. 31 (May 5, 2020): 155–74. http://dx.doi.org/10.24261/2183-816x0931.
Повний текст джерелаАнотація:
O rompimento da barragem construída pela mineradora brasileira Vale, que devastou a cidade de Brumadinho (MG) em janeiro de 2019, é o tema de seis charges que compõem o corpus do presente artigo. Sob a perspectiva de análise do discurso semiolinguística, as charges são gêneros discursivos oriundos de um contrato comunicativo midiático, equilibrado, como tal, entre duas intenções principais: informar e captar o leitor. Driblando, contudo, a objetividade e credibilidade típicas da mídia, as charges narram uma versão pessoal e crítica da realidade, expressa em uma verbo-visualidade “carregada” de opinião, humor e ironia. Veremos, pois, de que maneira tais textos manifestam a temporalidade por meio de mecanismos linguísticos e simbólicos das histórias em quadrinhos, que lhes permitem romper a aparente fixidez de sua estrutura.
Дисертації з теми "Equilibrage des charge"
1
Quintin, Jean-noël. "Equilibrage de charge dynamique sur plates-formes hiérarchiques." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00661447.
Повний текст джерелаАнотація:
La course à l'augmentation de la puissance de calcul qui se déroule depuis de nombreuses années entre les différents producteurs de matériel a depuis quelques années changé de visage: nous assistons en effet désormais à une véritable démocratisation des machines parallèles avec une complexification sans cesse croissante de la structure des processeurs. À terme, il est tout à fait envisageable de voir apparaître pour le grand public des architecture pleinement hétérogènes composées d'un ensemble de cœurs reliés par un réseau sur puce. La parallélisation et l'exécution parallèle d'applications sur les machines à venir soulèvent ainsi de nombreux problèmes. Parmi ceux-ci, nous nous intéressons ici au problème de l'ordonnancement d'un ensemble de tâches sur un ensemble de cœurs, c'est à dire le choix de l'affectation du travail à réaliser sur les ressources disponibles. Parmi les méthodes existantes, on distingue deux types d'algorithmes: en-ligne et hors-ligne. Les algorithmes en-ligne comme le vol de travail présentent l'avantage de fonctionner en l'absence d'informations sur le matériel ou la durée des tâches mais ne permettent généralement pas une gestion efficace des communications. Dans cette thèse, nous nous intéressons à l'ordonnancement de tâches en-ligne sur des plates-formes complexes pour lesquelles le réseau peut, par des problèmes de congestion, limiter les performances. Plus précisément, nous proposons de nouveaux algorithmes d'ordonnancement en-ligne, basés sur le vol de travail, ciblant deux configurations différentes. D'une part, nous considérons des applications pour lesquelles le graphe de dépendance est connu à priori. L'utilisation de cette information nous permet ainsi de limiter les quantités de données transférées et d'obtenir des performances supérieures aux meilleurs algorithmes hors-ligne connus. D'autre part, nous étudions les optimisations possibles lorsque l'algorithme d'ordonnancement connaît la topologie de la plate-forme. Encore une fois, nous montrons qu'il est possible de tirer parti de cette information pour réaliser un gain non-négligeable en performance. Nos travaux permettent ainsi d'étendre le champ d'application des algorithmes d'ordonnancement vers des architectures plus complexes et permettront peut-être une meilleure utilisation des machines de demain.
2
Quintin, Jean-Noël. "Equilibrage de charge dynamique sur plates-formes hiérarchiques." Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENM066/document.
Повний текст джерелаАнотація:
La course à l'augmentation de la puissance de calcul qui se déroule depuis de nombreuses années entre les différents producteurs de matériel a depuis quelques années changé de visage: nous assistons en effet désormais à une véritable démocratisation des machines parallèles avec une complexification sans cesse croissante de la structure des processeurs. À terme, il est tout à fait envisageable de voir apparaître pour le grand public des architecture pleinement hétérogènes composées d'un ensemble de cœurs reliés par un réseau sur puce. La parallélisation et l'exécution parallèle d'applications sur les machines à venir soulèvent ainsi de nombreux problèmes. Parmi ceux-ci, nous nous intéressons ici au problème de l'ordonnancement d'un ensemble de tâches sur un ensemble de cœurs, c'est à dire le choix de l'affectation du travail à réaliser sur les ressources disponibles. Parmi les méthodes existantes, on distingue deux types d'algorithmes: en-ligne et hors-ligne. Les algorithmes en-ligne comme le vol de travail présentent l'avantage de fonctionner en l'absence d'informations sur le matériel ou la durée des tâches mais ne permettent généralement pas une gestion efficace des communications. Dans cette thèse, nous nous intéressons à l'ordonnancement de tâches en-ligne sur des plates-formes complexes pour lesquelles le réseau peut, par des problèmes de congestion, limiter les performances. Plus précisément, nous proposons de nouveaux algorithmes d'ordonnancement en-ligne, basés sur le vol de travail, ciblant deux configurations différentes. D'une part, nous considérons des applications pour lesquelles le graphe de dépendance est connu à priori. L'utilisation de cette information nous permet ainsi de limiter les quantités de données transférées et d'obtenir des performances supérieures aux meilleurs algorithmes hors-ligne connus. D'autre part, nous étudions les optimisations possibles lorsque l'algorithme d'ordonnancement connaît la topologie de la plate-forme. Encore une fois, nous montrons qu'il est possible de tirer parti de cette information pour réaliser un gain non-négligeable en performance. Nos travaux permettent ainsi d'étendre le champ d'application des algorithmes d'ordonnancement vers des architectures plus complexes et permettront peut-être une meilleure utilisation des machines de demainThe race towards more processing power between all different hardware manufacturers has in recent years faced deep changes. We see nowadays a huge development in the use of parallel machines with more and more cores and increasingly complex architectures. It seems now clear that we will witness in a near future the development of cheap Network On Chip computers. Executing parallel applications on such machines raises several problems. Amongst them we take in this work interest in the problem of scheduling a set of tasks on a set of computing resources. Between all existing methods we can generally distinguish on-line or off-line algorithms. On-line algorithms like work-stealing present the advantage to work without informations on hardware or tasks durations but do not generally achieve an efficient control of communications. In this book we take interest in on-line tasks scheduling on complex platforms where networking can impact (through congestion) performance. More precisely, we propose several new scheduling algorithms based on work-stealing targeting two different configurations. In a first study, we consider applications whose dependency graph is known in advance. By taking advantage of this information we manage to limit the amount of data transfered and thus to achieve high performance and even outperform the best known off-line algorithms. Concurrently to that, we also study possible optimisations in the case where knowledge of platform topology is available. We show again that it is possible to use this information to enhance performance. Our work allows therefore to extend the application field of scheduling algorithms towards more complex architectures and we hope will allow a better use of tomorrow's machine
3
Renard, Hélène. "Equilibrage de charge et redistribution de données sur plates-formes hétérogènes." Phd thesis, Ecole normale supérieure de lyon - ENS LYON, 2005. http://tel.archives-ouvertes.fr/tel-00012133.
Повний текст джерелаАнотація:
Dans cette thèse, nous nous sommes intéressée à la mise en oeuvre d'algorithmes itératifs sur des grappes hétérogènes. Ces algorithmes fonctionnent avec un volume important de données (calcul de matrices, traitement d'images, etc.), qui sera réparti sur l'ensemble des processeurs. À chaque itération, des calculs indépendants sont effectués en parallèle et certaines communications ont lieu. Il n'existe pas de raison a priori de réduire le partitionnement des données à une unique dimension et de ne l'appliquer que sur un anneau de processeurs unidimensionnel. Cependant, un tel partitionnement est très naturel et nous montrerons que trouver l'optimal est déjà très difficile. Après cette étude sur le placement et l'équilibrage de charge pour plates-formes hétérogènes, nous nous sommes intéressée à la redistribution de données sur ces mêmes plates-formes, lorsque que les caractéristiques de ces dernières changent. En ce qui concerne les anneaux de processeurs homogènes, nous avons totalement résolu le problème : nous avons obtenu des algorithmes optimaux et prouvé leur exactitude dans le cas homogène et dans le cas hétérogène. En ce qui concerne les anneaux hétérogènes, le cas unidirectionnel a été totalement résolu, alors que le cas bidirectionnel reste ouvert. Cependant, sous l'hypothèse de redistribution légère, nous sommes capable de résoudre le problème de manière optimale.
4
Juganaru, Mihaela. "Equilibrage et régulation de charge dans les machines parallèles à mémoire distribuée." Phd thesis, Ecole Nationale Supérieure des Mines de Saint-Etienne, 1999. http://tel.archives-ouvertes.fr/tel-00822691.
Повний текст джерелаАнотація:
La résolution du problème d'allocation de charge représente un enjeu important dans l'exploitation des machines parallèles. Nous faisons d'abord une étude bibliographique de ce problème dans le cadre des architectures à mémoire distribuée en mettant l'accent sur l'allocation dynamique, plus précisément sur l'équilibrage et la régulation de charges régulières. Une stratégie originale de régulation basée sur un calcul de préfixe généralisé est proposée. Elle s'avère à la fois correcte, exacte et indépendante du réseau d'interconnexion de processeurs. Un noyau de régulation de charge basé sur cette stratégie est développé. Nous poursuivons ensuite avec une analyse de son temps total d'exécution. Nous trouvons qu'une loi de probabilité de Gumbel modélise le temps maximal d'exécution. A partir de ce résultat nous inférons des politiques d'initiation et de décision pour la mise en oeuvre de là stratégie proposée. L'algorithme de régulation ainsi obtenu est donc efficace. Une application de simulation des phénomènes mécaniques, déformation-recristallisation à chaud des agrégats polycristallins, est développée. Pour cette application dynamique nous utilisons le noyau de régulation de charge avec les politiques d'initiation et décision proposés. L'algorithme complet s'avère en pratique correct, stable et efficace.
5
Phan, Hoang Anh. "Equilibrage de charge et diffusion multicast dans les systèmes pair-à-pair." Paris 7, 2010. http://www.theses.fr/2010PA077123.
Повний текст джерелаАнотація:
Les systèmes pair-à-pair (P2P: Peer-to-Peer) mettent en relation des utilisateurs afin de mutualiser des ressources dans un environnement dynamique. Plusieurs types de systèmes P2P décentralisés construisent un réseau logique basé sur un graphe de de Bruijn, et offrent un bon compromis entre la taille du réseau et le degré moyen d'un nœud, avec un algorithme de routage simple, ils ne permettent cependant pas d'équilibrer efficacement la charge du réseau et ne supportent pas certains types de flux qui prennent de plus en plus d'importance dans l'Internet, telle la diffusion multicast. Cette thèse propose des améliorations à ces systèmes, et un support efficace de la diffusion multicast. Une première contribution consiste à améliorer le protocole D2B d-dimensionnel. Il est d'abord décrit en détails, puis des solutions aux problèmes de cohérence du réseau (liées à sa dynamicité) et de tolérance de pannes sont proposées. Une deuxième contribution concerne l'équilibrage de charge dans de tels systèmes. Les principales méthodes d'équilibrage de charge existantes sont d'abord décrites, avant de présenter nos solutions d'équilibrage du degré des nœuds. Une troisième et dernière contribution est consacrée à la diffusion multicast dans un système P2P, au niveau application. Après une introduction aux principales méthodes existantes, notre concept de "tree-farm" est présenté. Il permet de construire des familles d'ensembles d'arbres intérieur-disjoints pour la diffusion multicast dans un système P2P basé sur un graphe de de Bruijn. Les trois contributions sont évaluées à l'aide de simulations et comparées avec les méthodes de référence de l'état de l'artWithin a Peer-to-Peer (P2P) Systems a large number of users interact ail together in order to gather ressources in a dynamic environnement. Several decentralized P2P Systems construct an overlay network based on a de Bruijn graph, and offer a good tradeoff between network diameter and node average degree, with a simple routing algorithm. However, they do not efficiently balance the network's load and do not support some more and more popular kinds of communications in the internet such as multicast. This thesis work proposes significant improvements to these Systems, and an efficient multicast algorithm. A first contribution is the improvement of the d-dimensional D2B protocol. First, we describe the protdcol in detail, and then we propose solutions to problems of network coherence (related to its dynamîcity) and to fault tolerance. A second contribution relates to load balancing in such Systems. After the description of the main existing load balancing methods, we present our solutions for balancing the nodes1 degrees. A third and final contribution is dedicated to multicast in a P2P System, at the application level. After a short state of the art of existing methods, we present our concept of "tree-farm". This solution allows for building families of sets of interior-noeud-disjoint trees for efficient multicast communications in P2P Systems based on de Bruijn graphs. The three contributions are evaluated by means of simulations and compared with existing methods of the state of the art
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Pierson, Jean-Marc. "Equilibrage de charge dirige par les donnees. Applications a la synthese d'images." Lyon, École normale supérieure (sciences), 1996. http://www.theses.fr/1996ENSL0032.
Повний текст джерелаАнотація:
L'equilibrage de charge est un point crucial dans l'utilisation des machines paralleles. Nous etudions dans cette these le partitionnement rectilineaire qui constitue une solution a l'equilibrage des charges quand les donnees sont soumises a des contraintes de localite (le calcul associe a une donnee fait intervenir des donnees voisines). Nous nous attachons en particulier a apprecier la qualite de l'equilibrage de deux heuristiques de partitionnement. Nous montrons egalement la pertinence de ces approches a un equilibrage dynamique de la charge. Des applications dans le domaine de la synthese d'images (systeme de particules, calculs d'animations) montrent l'adequation de notre approche aux problemes poses par des structures de donnees irregulieres. Nous exposons egalement le travail fourni dans le developpement d'une bibliotheque parallele portable et son extension a en environnement graphique distribue
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Pérotin, Matthieu. "Calcul haute performance sur matériel générique." Thesis, Tours, 2008. http://www.theses.fr/2008TOUR4022/document.
Повний текст джерелаАнотація:
Un double constat motive ce travail: la demande en calcul haute performance des chercheurs et la faible utilisation moyenne de la puissance des ressources pédagogiques. Le problème a été de répondre à cette demande, tout en préservant les ressources pédagogiques pour les enseignements. Une solution simple et transparente pour les utilisateurs finaux a été recherchée. Les besoins des utilisateurs ont mené à un cahier des charges dont la plupart des contraintes sont satisfaites par l'utilisation d'une pile logicielle judicieuse. D'autres ne peuvent être résolues par la seule utilisation de solutions existantes et définissent un problème d'ordonnancement, où il faut répartir les processus soumis sur les ressources des salles de TPs. Plusieurs heuristiques ont été proposées pour le résoudre. Elles ont été comparées à l'aide d'un simulateur, puis implémentée sur une plateforme expérimentaleTwo facts are motivating this work: the demand for High Performance Computing of researchers and the low usage of the computing power of the pedagogic ressources. This thesis aims at giving an answer to the demand for HPC, while preserving the pedagogic ressources for the teaching. This work looked for a solution that would be simple and straightforward for the final users. Their needs and wishes lead to the definition of some specifications, in which most of the constraints could be satisfied with the use of a well designed software stack. Some others, however, cannot be satisfied with the use of existing solutions only, they define a new scheduling problem, in which the goal is to schedule the processes on the available ressources. This problem was studied and solved with various heurisitcs, which performances were compared with a simulator before being implemented in an experimental setup
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Renard, Hélène. "Équilibrage de charge et redistribution de données sur plates-formes hétérogènes." Lyon, École normale supérieure (sciences), 2005. http://www.theses.fr/2005ENSL0344.
Повний текст джерелаАнотація:
Dans cette thèse, nous nous sommes intéressée à la mise en oeuvre d'algorithmes itératifs sur des grappes hétérogènes. Ces algorithmes fonctionnent avec un volume important de données (calcul de matrices, traitement d'images, etc. ), qui sera réparti sur l'ensemble des processeurs. À chaque itération, des calculs indépendants sont effectués en parallèle et certaines communications ont lieu. Prenons l'exemple d'une matrice rectangulaire de données : l'algorithme itératif fonctionne répétitivement sur cette matrice, divisée en tranches verticales (ou horizontales) allouées aux processeurs. À chaque étape de l'algorithme, les tranches sont mises à jour localement et les informations frontières sont échangées entre tranches consécutives. Cette contrainte géométrique implique que les processeurs soient organisés en anneau virtuel. Chaque processeur communique seulement deux fois, une fois avec son prédécesseur (virtuel) dans l'anneau et une fois avec son successeur. Il n'existe pas de raison a priori de réduire le partitionnement des données à une unique dimension et de ne l'appliquer que sur un anneau de processeurs unidimensionnel. Cependant, un tel partitionnement est très naturel et nous montrerons que trouver l'optimal est déjà très difficile. Après cette étude sur le placement et l'équilibrage de charge pour plates-formes hétérogènes, nous nous sommes intéressée à la redistribution de données sur ces mêmes plates-formes, lorsque que les caractéristiques de ces dernières changent. En ce qui concerne les anneaux de processeurs homogènes, nous avons totalement résolu le problème : nous avons obtenu des algorithmes optimaux et prouvé leur exactitude dans le cas homogène et dans le cas hétérogène. En ce qui concerne les anneaux hétérogènes, le cas unidirectionnel a été totalement résolu, alors que le cas bidirectionnel reste ouvert. Cependant, sous l'hypothèse de redistribution légère, nous sommes capable de résoudre le problème de manière optimaleIn this thesis, we study iterative algorithms onto heterogeneous platforms. These iterative algorithms operate on large data samples (recursive convolution, image processing algorithms, etc. ). At each iteration, independent calculations are carried out in parallel, and some communications take place. An abstract view of the problem is the following: the iterative algorithm repeatedly operates on a large rectangular matrix of data samples. This data matrix is split into vertical (or horizontal) slices that are allocated to the processors. At each step of the algorithm, the slices are updated locally, and then boundary information is exchanged between consecutive slices. This (virtual) geometrical constraint advocates that processors be organized as a virtual ring. Then each processor will only communicate twice, once with its (virtual) predecessor in the ring, and once with its successor. Note that there is no reason a priori to restrict to a uni-dimensional partitioning of the data, and to map it onto a uni-dimensional ring of processors. But uni-dimensional partitionings are very natural for most applications, and, as will be shown in this thesis, the problem to find the optimal one is already very difficult. After dealing with the problems of mapping and load-balancing onto heterogeneous platforms, we consider the problem of redistributing data onto these platforms, an operation induced by possible variations in the resource performances (CPU speed, communication bandwidth) or in the system/application requirements (completed tasks, new tasks, migrated tasks, etc. ). For homogeneous rings the problem has been completely solved. Indeed, we have designed optimal algorithms, and provided formal proofs of correctness, both for unidirectional and bidirectional rings. For heterogeneous rings there remains further research to be conducted. The unidirectional case was easily solved, but the bidirectional case remains open. Still, we have derived an optimal solution for light redistributions, an important case in practice
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Haj, Mahmoud Yanal. "Modélisation et évaluation de performances des systèmes de distribution de charge en environnements répartis." Paris 6, 1999. http://www.theses.fr/1999PA066664.
Повний текст джерела
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Vuchener, Clement. "Equilibrage de charges dynamique avec un nombre variable de processeurs basé sur des méthodes de partitionnement de graphe." Thesis, Bordeaux, 2014. http://www.theses.fr/2014BORD0012/document.
Повний текст джерелаАнотація:
L'équilibrage de charge est une étape importante conditionnant les performances des applications parallèles. Dans le cas où la charge varie au cours de la simulation, il est important de redistribuer régulièrement la charge entre les différents processeurs. Dans ce contexte, il peut s'avérer pertinent d'adapter le nombre de processeurs au cours d'une simulation afin d'obtenir une meilleure efficacité, ou de continuer l'exécution quand toute la mémoire des ressources courantes est utilisée. Contrairement au cas où le nombre de processeurs ne varie pas, le rééquilibrage dynamique avec un nombre variable de processeurs est un problème peu étudié que nous abordons ici.Cette thèse propose différentes méthodes basées sur le repartitionnement de graphe pour rééquilibrer la charge tout en changeant le nombre de processeurs. Nous appelons ce problème « repartitionnement M x N ». Ces méthodes se décomposent en deux grandes étapes. Dans un premier temps, nous étudions la phase de migration et nous construisons une « bonne » matrice de migration minimisant plusieurs critères objectifs comme le volume total de migration et le nombre total de messages échangés. Puis, dans un second temps, nous utilisons des heuristiques de partitionnement de graphe pour calculer une nouvelle distribution optimisant la migration en s'appuyant sur les résultats de l'étape précédente. En outre, nous proposons un algorithme de partitionnement k-aire direct permettant d'améliorer le partitionnement biaisé. Finalement, nous validons cette thèse par une étude expérimentale en comparant nos méthodes aux partitionneursactuelsLoad balancing is an important step conditioning the performance of parallel programs. If the workload varies drastically during the simulation, the load must be redistributed regularly among the processors. Dynamic load balancing is a well studied subject but most studies are limited to an initially fixed number of processors. Adjusting the number of processors at runtime allows to preserve the parallel code efficiency or to keep running the simulation when the memory of the current resources is exceeded.In this thesis, we propose some methods based on graph repartitioning in order to rebalance the load while changing the number of processors. We call this problem \M x N repartitioning". These methods are split in two main steps. Firstly, we study the migration phase and we build a \good" migration matrix minimizing several metrics like the migration volume or the number of exchanged messages. Secondly, we use graph partitioning heuristics to compute a new distribution optimizing the migration according to the previous step results. Besides, we propose a direct k-way partitioning algorithm that allows us to improve our biased partitioning. Finally, an experimental study validates our algorithms against state-of-the-art partitioning tools
Книги з теми "Equilibrage des charge"
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1951-, Peters Robert L., and Lovejoy Thomas E, eds. Global warming and biological diversity. New Haven, CT: Yale University Press, 1992.
Знайти повний текст джерелаЧастини книг з теми "Equilibrage des charge"
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Gianinetti, Alberto. "Some Special Instances of Entropy Change." In An Account of Thermodynamic Entropy, 144–48. BENTHAM SCIENCE PUBLISHERS, 2017. http://dx.doi.org/10.2174/9781681083933117010020.
Повний текст джерелаАнотація:
A few particular phenomena are quite difficult to frame into the fundamental equation, nonetheless they can be interpreted to the light of the general idea of statistical mechanics that any system and any overall change tend to the most probable state, i.e., a state that is microscopically equilibrated and then macroscopically stable.
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Pitman, Justin T. "Dizziness on Airplane." In Acute Care Casebook, edited by N. Stuart Harris, 16–19. Oxford University Press, 2018. http://dx.doi.org/10.1093/med/9780190865412.003.0004.
Повний текст джерелаАнотація:
There is a broad differential for dizziness in any environment. Assessing a thorough history, concurrent medical problems, and careful physical examination can often narrow the possible causes significantly. In the setting of ear pain and recent altitude or pressure change, barotrauma should be suspected. Although most care is supportive, including the use of nonsteroidal anti-inflammatory drugs, the Frenzel maneuver and decongestants can help equilibrate inner ear and atmospheric pressures. This chapter examines the case of a woman who presents to the emergency room with ear pain following a recent airplane trip and addresses the patient history, details of the physical exam, diagnosis, and treatment plan.
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Sørensen, Georg, Jørgen Møller, and Robert Jackson. "11. Major Issues in IR: Climate Change, Terrorism, Religion, Power and Hegemony." In Introduction to International Relations: Theories and Approaches, 309–49. Oxford University Press, 2021. http://dx.doi.org/10.1093/hepl/9780198862208.003.0011.
Повний текст джерелаАнотація:
This chapter examines four of the most important issues in international relations (IR): climate change, international terrorism, religion, and balance and hegemony in world history. It also considers the different ways in which these issues are analysed by the various theories presented in this book. The chapter begins with a discussion of what the issue is about in empirical terms, the problems raised and why they are claimed to be important, and the relative significance of the issue on the agenda of IR. It then explores the nature of the theoretical challenge that the issues present to IR and how classical and contemporary theories handle the analysis of these issues. The chapter addresses how climate change has become a first order challenge of international relations and IR theories, Samuel Huntington’s ‘clash of civilizations’ thesis, the influence of religion on politics, and how throughout history different state systems have come to equilibrate on either balance of power or hegemony.
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Sheppard, Charles. "8. Global scale pressures on reefs—climate change." In Coral Reefs: A Very Short Introduction, 102–11. Oxford University Press, 2021. http://dx.doi.org/10.1093/actrade/9780198869825.003.0008.
Повний текст джерелаАнотація:
Ocean temperatures are rising. This is critical for corals and other reef organisms because most live very close to their thermal limits already. The rise is caused by the greenhouse effect from increasing CO2 emissions. Superimposed on a general background rise caused by the general increase in heat content of the world are pulses—ocean heatwaves—caused by vagaries in ocean circulation. Globally, this is now the greatest threat to reefs. Warming pulses cause mass coral bleaching and mortality when the overstressed symbiotic algae are expelled from the corals, showing the white limestone beneath the now transparent coral tissue. All coral reef areas of the world now exhibit mass bleaching events. Recovery of a reef is possible, but only if given some decades of stable temperatures, and predictions are that warming events are occurring increasingly frequently and are of increasing severity. Coral cover on reefs in all reef areas is declining sharply. Seawater also becomes increasingly acidic, which impedes coral calcification. Added to this, there is a lag of 20–40 years for carbon dioxide in the air to equilibrate with the ocean, so even were there to be a cessation in the rise in the atmosphere today, these effects would continue to develop for a few decades more. 350 parts per million CO2 is considered to be a threshold concentration for calcification to be possible but already the atmosphere is at about 415 ppm. Sea levels are rising too as a result, and reefs are degrading and losing their ability to act as breakwaters.
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Walker, James C. G. "How to Solve a Nonlinear System." In Numerical Adventures with Geochemical Cycles. Oxford University Press, 1991. http://dx.doi.org/10.1093/oso/9780195045208.003.0006.
Повний текст джерелаАнотація:
In a linear system the expressions, yp, for rates of change are linear functions of the dependent variables, y. More complicated functions of y do not appear, not even products of the dependent variables like y1 * y2. But most theoretical problems in Earth system science involve nonlinearities. For example, the rate at which a chemical reaction consumes species 1 may be proportional to the product of the concentrations of species 1 and the species 2 with which it is reacting, y1 * y2. In this chapter I shall describe and solve a simple nonlinear system involving the reaction between dissolved oxygen and organic carbon in the deep sea. I shall show how the nonlinear system can be represented by a linear system, provided that changes in the dependent variables are made in sufficiently small increments. Such increments are kept small by stepping forward in time with small steps. The time step can be adjusted automatically during the calculation so as to keep the increments small enough but no smaller than necessary. Steps that are too large cause errors or even instability, and steps that are too small waste time. The representation of a nonlinear system by its linear equivalent (for small increments) calls on algebraic manipulations that can be tedious and a prolific source of mistakes in complicated systems. This algebra can be avoided, however, by letting the computer perform the equivalent manipulations numerically. I shall demonstrate how to do this, finishing the chapter with a program that can solve coupled nonlinear systems directly from the equations for the rates of change of the dependent variables, automatically adjusting the time step to small values when the rates of change are large and to large values when the rates of change are small. Figure 4-1 shows a simple model of the processes that control the oxygen balance of the deep sea. Dissolved oxygen in surface seawater equilibrates with the atmosphere. Downwelling currents carry dissolved oxygen into the deep sea, where most of it reacts (metabolically) with organic matter carried into the deep sea in the form of settling particles of biological origin.
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West-Eberhard, Mary Jane. "Punctuation." In Developmental Plasticity and Evolution. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195122343.003.0038.
Повний текст джерелаАнотація:
In punctuated evolution (Eldredge and Gould, 1972) periods of relatively little change (“stasis”) are punctuated by episodes of relatively rapid change in the rate of evolution of a quantitative morphological trait, as seen in the fossil record of morphology. According to Simpson (1984), the term quantum evolution, refers to the same thing. Like Eldredge and Gould, Simpson contrasted quantum evolution with phyletic change, or sustained directional evolution without branching; considered that it could be associated with speciation (though also with phyletic evolution; p. 206); and even mentioned interrupted equilibra “In phyletic evolution equilibrium of the organism-environment system is continuous, or nearly so, although the point of equilibrium may and usually does shift. In quantum evolution equilibrium is lost, and a new equilibrium is reached”. I use the term “punctuation” rather than “quantum” because it less ambiguously describes change in rate of evolution. In its original meaning (from the Latin quantus), quantum means quantity. But quantum change, as mentioned by Simpson, is identified with the “quanta” of physics, which are discrete units of energy. This could encourage mistaken identification of punctuated change with the origin of discrete novelties, not the intended meaning of punctuated evolution, which is periodically altered rate of change in a continuously variable, quantitative trait. Mayr, Eldredge, Gould, and others (e.g., Stanley, 1979, 1981) explain stasis and punctuation in terms of speciation. Speciational punctuation hypotheses see stasis as due to the characteristics of established biological species, such as gene flow within interbreeding populations, large population size, heterogeneity of the species environment that retards directional change, developmental integration, canalization, coadapted genomes, stabilizing selection, and frequently reversing evolution over time within established species (Eldredge and Gould, 1997). These factors have been summarized by the term “gene-pool cohesiveness” (Mayr, 1989) or “developmental coherences” (Gould, 1989b), though the causes of stasis under the speciational hypothesis are admittedly vague and debatable (for reviews of other possible causes of stasis, see Williamson, 1987; Coyne and Charlesworth, 1997; Van Valen, 1982a; Spicer, 1993).
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Baer, Tomas, and William L. Hase. "Product Energy Distributions." In Unimolecular Reaction Dynamics. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195074949.003.0011.
Повний текст джерелаАнотація:
The measurement of product translational and rotational energies, and in some cases vibrational energy, is often more readily accomplished than the measurement of the dissociation rate. As a result there exists a considerable body of experimental information about product energy distributions (FED) for many classes of reactions. The only simple model for treating these FED is the statistical one; however, there is a considerable diversity in its application. In the dissociation of large molecules at moderate to large excess energies, the translational, rotational, and vibrational energy distributions can be treated as continuous functions. On the other hand, in the dissociation of triatomic molecules, it is often possible to measure the quantized rotational energy distribution for specific vibrational energy levels of the diatomic product. Just as in the determination of the dissociation rates, product energy partitioning is highly sensitive to the potential energy surface. If there is no reverse activation barrier, the product energies are often distributed statistically. That is, the distributions depend only upon the product phase space and are independent of the detailed shape of the potential energy surface. On the other hand, for reactions with a “tight” transition state located at the top of a reverse activation barrier, statistical redistribution of the product energies is often not possible. After passing through the transition-state region, the products move down the repulsive wall and rapidly dissociate with little chance to exchange and equilibrate the available energy. Often, such products are ejected with considerable translational energy. This happens in large as well as small molecules or ions. The resulting product energy partitioning is then highly nonstatistical, even though the dissociation rate is perfectly predicted by RRKM theory. That is, the dissociation rate and product energy partitioning are separate and uncoupled events. The rate is governed early in the reaction history by the structure of the transition state, while product energy partitioning is determined late in the reaction and is governed by the shape of the potential energy surface at large internuclear distances. The most effective model for treating product energy distributions (PEDs) of reactions with no reverse activation barriers is the statistical theory.
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Anderson, Greg M., and David A. Crerar. "Standard States." In Thermodynamics in Geochemistry. Oxford University Press, 1993. http://dx.doi.org/10.1093/oso/9780195064643.003.0016.
Повний текст джерелаАнотація:
At this point we have introduced the activity as a ratio of fugacities (Chapter 11). The fugacity of a constituent, in turn, we saw was a quantity very much like a vapor pressure or partial pressure, which is directly linked to the Gibbs free energy of that constituent, such that a ratio of fugacities leads directly to a difference in free energies. The fugacity was introduced as a means of dealing with gases and gaseous solutions, and it is measured by measuring gas volumes or densities. Nevertheless, there is nothing restricting its use to gaseous constituents, and we suggested that it is very useful to regard the fugacity as a state variable; as a property of any constituent of any system, solid, liquid, or gas, whether equilibrated with a gas or not, and whether measurable or not. This leads to the easiest approach to understanding activities. The activity of a constituent is the ratio of the fugacity of that constituent to its fugacity in some other state, which we called a reference state. We then showed through consideration of the Lewis Fugacity Rule, which is an extension of Dalton's Law, that for ideal solutions of condensed phases, the activity of a constituent equals its mole fraction, if the reference state is the pure constituent at the same P and T. Deviations from ideal behaviour are then conveniently handled by introducing Henryan and Raoultian activity coefficients. The utility of these relations would be quite sufficient for retaining the activity in our collection of thermodynamic parameters, but in fact the activity can be applied to a much wider range of conditions, simply by varying the choice of reference state. We now examine the various possible choices of this reference state, and the resulting equations and applications. In the most general sense, the fugacity and activity concepts satisfy the need to relate system compositions to free energy changes. That a single parameter, the activity, can do this for essentially any system is a tribute to its tremendous versatility.
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Sposito, Garrison. "Mineral Weathering." In The Chemistry of Soils. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780190630881.003.0009.
Повний текст джерелаАнотація:
Mineral weathering begins with mineral dissolution, typically as induced by protons or by ligands that form strong complexes with metals (Section 1.4). Proton-induced dissolution begins with H+ adsorption, exemplified in Eq. 3.2 for a metal oxyhydroxide mineral. In the absence of ligands that could replace the positively charged water molecule resulting from this rapid reaction, proton adsorption is followed by slow detachment of the metal, which then equilibrates as a soluble species in the soil solution, as illustrated in Fig. 5.1 (pathway 1) for gibbsite [Al(OH)3; see Fig. 2.7] at a pH value low enough that the detached Al3+ does not hydrolyze. Ligand-induced dissolution is also illustrated in Fig. 5.1 (pathway 2). The ligand is a fluoride anion, which forms a strong complex with Al3+ (see problem 3 in Chapter 4). Adsorption in this case occurs by ligand exchange, which is illustrated for carboxylate in Eq. 3.3. A similar reaction occurs for F-:...Slow detachment of the AlF2+ complex then follows. Whenever a mineral dissolution reaction induced by either of these two-step mechanisms is far from equilibrium, it is not influenced by the very low concentration of the constituent released from the dissolving mineral and its rate can be described by zero-order kinetics (Table 4.2). Accordingly, if [A] is the concentration of a constituent released, then the rate law can be expressed as...where kd is a rate coefficient independent of [A] , but a function of temperature, pressure, pH, the chemical properties of the mineral, and, if appropriate, the concentration of the ligand inducing dissolution via the second mechanism in Fig. 5.1. The mineral dissolution rate on the left side of Eq. 5.2 can be mass-normalized to express it in moles per mole of mineral per second by dividing the molar concentration [A] with the solids concentration of the mineral expressed in units of moles per liter. This mass-normalized rate does not depend on the amount of mineral dissolving. For proton-induced dissolution, the rate is then a function of temperature, pressure, pH, and the chemical nature of the mineral.
Тези доповідей конференцій з теми "Equilibrage des charge"
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Quinn, D. Dane, and Tom T. Hartley. "Influence of Charge Transfer Interconnection Topology on State of Charge Performance in Battery Packs: Simulation Results." In ASME 2012 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. American Society of Mechanical Engineers, 2012. http://dx.doi.org/10.1115/detc2012-71058.
Повний текст джерелаАнотація:
The performance of a battery pack, composed of multiple connected cells, can be increased with the additional of a charge balancing system. This work explores the dynamic performance of charge balancing systems and how their ability to equilibrate the state of charge depends on the design of the underlying charge balancing network. The performance of the charge balancing system is shown through simulation studies to be related to the properties of the underlying graph of the balancing connections.
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Chen, Yunfei, Zhonghua Ni, Guiming Wang, Dongyan Xu, and Deyu Li. "Molecular Dynamics Simulation of Electroosmotic Flow in Nanotubes." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41470.
Повний текст джерелаАнотація:
The ion distribution and electroosmotic flow of sodium chloride solutions confined in cylindrical nanochannels with different surface charge densities are studied with molecular dynamics (MD). In order to obtain simulation results corresponding to more realistic situations, the MD simulation consists of two steps. The first step is used to equilibrate the system and obtain a more realistic ion distribution in the solution under different surface charge densities; and the second step is to apply an electrical field to drive the liquid and extract the electroosmotic flow information. Simulation results indicate that a higher surface-charge density corresponds to a higher peak of the counter ion concentration. Predictions based on the continuum theory were also calculated and compared with the molecular dynamics results. Even though the continuum theory cannot reflect the molecular nature of ions and water molecules, it is found that for low surface charge densities, the continuum theory can still give reasonable results if modified boundary conditions are applied. Charge inversion under high surface charge density has been predicted and observed recently, however, the simulation results do not indicate charge inversion even for a surface density as high as −0.34 C/m2. This might be due to the fact that we perform the MD simulations with monovalent ions, which have a tendency to suppress charge inversion, as demonstrated in the recent literature.
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Gemmen, Randall S., and Christopher D. Johnson. "Thermal Gradient Induced Current Recirculation on Load Change in Solid Oxide Fuel Cells." In ASME 2006 4th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2006. http://dx.doi.org/10.1115/fuelcell2006-97187.
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This paper considers recent model results examining the transient performance of three common solid oxide fuel cell (SOFC) geometries (cross-flow, co-flow, and counter-flow) during load reduction events. Of particular note for large load decrease (e.g., shutdown) is the occurrence of reverse current over significant portions of the cell, starting from the moment of load loss up to the point where equilibrated conditions again provide positive current. This behavior results from the temperature gradients that exist in an SOFC stack. Also reported are test results from an experiment employing two separate button cells coupled together electrically (anode-to-anode and cathode-to-cathode) which are used to confirm the model predictions. The test results confirm the predictions of the model in that temperature gradients are a driver for current circulation within a cell. Also reported are test results of a button cell operated under reverse current to help begin to identify what effects such operation may have on fuel cell performance and durability.
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Finkbeiner, John, Charles Watkins, and Joel Koplik. "Molecular Dynamics Simulations of Thermo-Mechanical Effects in Nanodrop Impact." In ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/fedsm2014-21371.
Повний текст джерелаАнотація:
Nanodrop impact onto a solid substrate is of interest for nano-scale liquid-impingement, phase-change cooling and for material deposition processes. In the present study, classical molecular dynamics (MD) simulation techniques were implemented to study the thermo-mechanical properties of the impact of nanometer scale liquid droplets upon an atomistic substrate at a temperature higher than that of the droplet. The droplets were comprised of approximately 50,000 Lennard-Jones atoms arranged in tetramer finitely extensible non-linear elastic (FENE) chain molecules forming a sphere of 8 nm radius. They were equilibrated and then projected towards a wall, where we observed the response upon collision by changes in shape, temperature, and density gradients, across a variety of impingement velocities, substrate temperatures, and wetting conditions. The baseline cases of equal substrate and nano-drop temperature were validated by comparison with previously reported results. A reaction spectrum ranging from full thermal vaporization of the drop, with respective substrate cooling, to complete kinetic disintegration upon impact and surface heating are analyzed. The variation of thermal and kinetic effects across the parametric environment is used to identify those regimes that optimize heat transfer from the surface, as well as those that best facilitate material deposition processes.
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Churchwell, Lauren, and David DiCarlo. "Oil and Gas Relative Permeability as a Function of Fluid Composition." In SPE Improved Oil Recovery Conference. SPE, 2022. http://dx.doi.org/10.2118/209388-ms.
Повний текст джерелаАнотація:
Abstract During miscible gas injection for enhanced oil recovery, the composition of the fluids can change throughout the reservoir as the oil and gas phases develop miscibility. Measuring and modeling relative permeability as compositional regions are traversed creates many challenges. In simulators, the association of each phase with a relative permeability curve sometimes creates discontinuities when phases disappear across miscibility boundaries. Some newer relative permeability models attempt to resolve these issues by changing the standard "oil" and "gas" method of phase labeling and instead labeling phases according to a physical property that is continuous and tied to composition, most notably the fluid density or Gibbs free energy (GFE). Ideally, a relative permeability model will be based on experimental measurements. A handful of all relative permeability experiments focus on studying changes in relative permeability brought about by changes in fluid composition with increasing capillary number. However, there is also evidence to suggest that composition can impact relative permeability even at capillary numbers well below the capillary desaturation threshold. In this research, two-phase gas/oil core flood experiments were performed with ethane as the gas phase and equilibrated octane as the oil phase. Pressure was varied so that the composition (density and GFE) of the gas and oil were changing. The capillary numbers were kept low and constant to prevent capillary desaturation of the oil phase. The experiments were then repeated with an added residual brine phase to test the effect of composition with a third phase present. The results show that changing the density and GFE of the oil and gas phases in either two-phase or three-phase flow had no impact on the relative permeability curves. However, significant changes were observed when comparing two-phase to three-phase oil and gas relative permeabilities. When only gas and oil were flowing in the core, the oil phase formed a continuous layer on the pore surfaces. The addition of residual brine caused the oil to form droplets, reducing the relative permeability of both the oil and gas phases in the absence of a continuous layer of oil. These findings verify previous history-matched relative permeabilities in literature and show that the oil phase connectivity is more important than compositional parameters.
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Higashiyama, S., I. Ohkubo, H. Ishiguro, and M. Sasaki. "A NEW FUNCTION OF HUMAN KININOGENS: THE AMINO-TERMINAL REGION OF DOMAIN 1 INVOLVES AN EF HAND-LIKE STRACTURE FOR METAL BINDING." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1642851.
Повний текст джерелаАнотація:
Two types of kininogens in mammalian plasma, high molecular weight (HMW) and low molecular weight (LMW) kininogens, are the precursors of kinin. Especially, HMW kininogen circulates in the plasma as a complex with prekallikrein and factor XI, and functions as a cofactor in the initial phase reactions of intrinsic blood coagulation cascade. Recently, it has been found that the kininogens have inhibitory activity toward cysteine proteinases. The heavy chain portion, which is identical for HMW and LMW kininogens, is composed of three domains, domain 1, 2 and 3. Each the domain 2 and 3 has a reactive site as a cysteine proteinase inhibitor. However, physiological function of domain 1 remains still unknown. By using the antibody recognizing the interaction between HMW kininogen and Ca2+ (anti-HMW kininogen-Ca2+ antibody) as a probe, we newly found the Ca2+ binding site in the domain 1.Anti-HMW kininogen-Ca2+ antibody was isolated from anti-HMW kininogen antiserum as an antibody which bound to a HMW kininogen-Sepharose column equilibrated with 40 mM Tris-HCl buffer, pH 7.5, containing 1.0 M NaCl and 1 mM CaCl2, and was eluted with 3 mM EDTA. Resulting from the characterization by ELISA, this antibody specifically recognized the CB-1 region (CNBr-cleavage fragment 1: 1-160 amino acid sequence) of the heavy chain of kininogen molecules in the presence of Ca2+ or Mg2+. Furthermore, circular dichroism (CD) experiments showed that the conformational changes of HMW kininogen and heavy chain were induced by the addition of metal ions such as Ca2+ or Mg2+, and that this change was due to the conformational change of the CB-1 region. The dissociation constant (Kd) for heavy chain measured by Ca2+ titration analysis by CD at 214 nm was found to be 0.33 ± 0.09 mM. The number of Ca2+ binding sites of heavy chain calculated from Hill plot was 1.15 ± 0.04. The EF handlike structure found in the amino-terminal portion of the heavy chain of kininogen molecules strongly supported the above data. This indicates a possibility that kininogens play an important role as a Ca2+ binding protein.
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Mollaeian, Keyvan, Yi Liu, and Juan Ren. "Investigation of Nanoscale Poroelasticity of Eukaryotic Cells Using Atomic Force Microscopy." In ASME 2017 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/dscc2017-5254.
Повний текст джерелаАнотація:
Intracellular network deformation of the cell plays an important role in cellular shape formation. Recent studies suggest that cell reshaping and deformation due to external forces involves cellular volume, pore size, elasticity, and intracellular filaments polymerization rate changes. This behavior of live cells can be described by poroelastic models because of the porous structure of the cytoplasm. In this study, the poroelasticity of human mammary basel/claudin low carcinoma cell (MDA-MB-231) was investigated using indentation-based atomic force microscopy. The effects of cell deformation (i.e., indentation) rate on the poroelasticity of MDA-MB-231 cells were studied. Specifically, the cell poroelastic behavior (i.e., the diffusion coefficient) was quantified at different indenting velocities (0.2, 2, 10, 20, 100, 200 μm/s) by fitting the force-relaxation curves using a poroelastic model. It was found that the in general the MDA-MB-231 cells behaved poroelastic, and they were less poroelastic (i.e., with lower diffusion coefficient) at higher indenting velocities due to the local stiffening up caused by faster force loads. Poor poroelastic relaxation was observed when the indenting velocity was lower than 10 μm/s due to the intracelluar fluid redistribution during the slow indenting process to equilibrate the intracellular pressure. Moreover, the measurement results showed that the pore size reduction caused by local stiffening at faster indenting velocities is more dominant than the Young’s modulus in affecting the cell poroelasticity.
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Sinha, Shashank, Jonathan B. Freund, and Vijay K. Dhir. "Molecular Dynamics Simulation of Interfacial Tension of Ultra-Thin Liquid Films on a Solid Surface." In ASME 2001 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2001. http://dx.doi.org/10.1115/imece2001/htd-24203.
Повний текст джерелаАнотація:
Abstract The effect of wall proximity on the interfacial tension of ultra-thin liquid films of Lennard-Jones (12,6) fluid has been studied using Molecular Dynamics Simulation. The wall’s presence can potentially affect drop-wise condensation and other phase change phenomena such as boiling. Initially the Lennard-Jones atoms are placed near a solid wall with FCC lattice structure in a doubly periodic box. Once equilibrated at a desired temperature, a thin liquid film forms on the solid wall. The surface tension of the liquid-vapor interface is computed statistically. When the film is thick (> 40 Å), surface tension at the liquid-vapor interface is found to be unaffected by the presence of the solid wall and matches bulk values reported for Argon. However for thinner films (< 15 Å), surface tension of the liquid-vapor interface deviates from the macroscopic value. This has been investigated for various temperatures ranging from the triple point to the critical point. As the film thins further (1–2 molecules thickness), the liquid-vapor interface resembles a solid-vapor interface. Surface tension of this solid-vapor interface is evaluated for a solid wall modeled both by an equivalent interacted potential and discrete atoms. The two cases are found to yield different results. The Equivalent potential for the wall gives lower surface tension and liquid density near the solid wall compared to the discrete atoms case.
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verhallen, P. F. J., E. M. Bevers, P. Comfurius, W. M. A. Linkskens, and R. F. A. Zwaal. "CALPAIN-MEDIATED CYTOSKELETAL DEGRADATION CORRELATES WITH STIMULATION OF PLATELET PROCOAGULANT ACTIVITY." In XIth International Congress on Thrombosis and Haemostasis. Schattauer GmbH, 1987. http://dx.doi.org/10.1055/s-0038-1642821.
Повний текст джерелаАнотація:
We have shown earlier that the negatively charged phospholipid phosphatidylserine (PS), which becomes translocated from the inner surface to the outer surface of the plasma membrane upon platelet activation, is responsible for platelet procoagulant activity. Studies with erythrocytes have suggested a role for cytoskeletal proteins in the regulation of transmembrane asymmetry of PS. The possibility that platelet cytoskeletal proteins are involved in the loss of transmembrane asymmetry of PS, was explored by correlative investigations of both platelet prooagulant activity and activity of calpain, an endogenous Ca 2+ -dependent thiol-protease, known to hydrolyze major cytoskeletal proteins (e.g.: filamin, talin, myosin). Platelet procoagulant activity was assayed by determination of the prothrombinase activity under conditions at which the catalytic PS-surface was rate-limiting. Calpain-activity was monitored by the appearance of known degradation products of major cytoskeletal proteins. The following results were obtained: (1) The ability of thrombin, collagen, collagen & thrombin, or the Ca -ionophore A23187 to stimulate platelet procoagulant activity closely correlated with their ability to stimulate platelet calpain-activity (2). Generation of platelet procoagulant activity upon platelet stimulation by collagen & thrombin or by A23187 exhibited a time course identical to the development of calpain-activity. In addition, the local anesthetics dibucaine and tetracaine, shown to gradually stimulate calpain activity, were able to generate platelet procoagulant activity with a similar time course. (3) Using a Ca2+ buffering system and A23187 to equilibrate intracellular- and extracellular free Ca2+ , it was found that the Ca2+ -response relationship of both platelet calpain- and pro-coagulant-activity was identical. From these findings we conclude that the degradation of cytoskeletal proteins destroys their putative interactions with PS, enabling this lipid to participate in transbilayer movement, leading to the formation of a procoagulant outer surface of the platelet.
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Alapati, Raghava, Dorel Moldovan, and Ram V. Devireddy. "Asymmetry of Structural Characteristics of Lipid Bilayers Induced by Dimethylsulfoxide: An Atomistic Simulation Study." In ASME 2008 Summer Bioengineering Conference. American Society of Mechanical Engineers, 2008. http://dx.doi.org/10.1115/sbc2008-192813.
Повний текст джерелаАнотація:
In a typical cryopreservation protocol, the system to be preserved is first equilibrated with chemicals known as cryoprotective agents (CPAs). CPAs have been shown to alleviate cell damage from either the solute effects or the formation of intracellular ice during the subsequent freezing process. Thus, an extensive body of literature reporting the effects of CPAs on cellular systems has been accumulated over the last 50 years; detailing largely experimental interactions between cell systems and chemicals. Recent advances in computational methodology now offer an additional dimension in our ability to understand the molecular interactions between cell membranes, idealized as lipid bilayers and CPAs at atomistic scales. Computer simulations provide unique capabilities for analyzing biomembrane properties from atomistic perspective with a degree of detail that is hard to reach by other techniques. The excellent agreement with the experiment obtained in various molecular dynamics (MD) studies [1] on simple model membranes has raised the confidence in applying the molecular dynamics simulations to even more complex systems. Dimethylsulfoxide (DMSO) is one of the most widely used solvents in cell biology and cryopreservation. During a typical cryopreservation protocol the DMSO composition of aqueous buffers inside and outside of the cell is known to differ considerably. To model and understand the structural changes in cell membranes in such a situation we performed MD simulations of an idealized lipid bilayer membrane which separates two aqueous reservoirs with and without DMSO. Zwitterionic dimyritoylphosphatidylcholine (DMPC) lipid bilayers was chosen as the model membrane.