Academic literature on the topic 'Distribution de charges non uniforme'
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Journal articles on the topic "Distribution de charges non uniforme"
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Pshchelko, Nikolai, and Ekaterina Vodkailo. "Features of Electrostatic Fields and Their Force Action When Using Micro- and Nanosized Inter-Electrode Gaps." Materials 13, no. 24 (December 11, 2020): 5669. http://dx.doi.org/10.3390/ma13245669.
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The present work is devoted to assessing the influence of discreteness of electric charge distribution in the double electric layer on the characteristics of the electric fields and their force action in capacitor structures with small interelectrode gaps. Due to the fact that modern technologies often use submicron-sized interelectrode gaps, it is no longer possible to consider the electrodes uniformly charged because of the discreteness of the electric charge. The corresponding development of a mathematical and physical model for the study of a non-uniform electric field is suggested. Numerical calculations are carried out, expressions, criteria, and results that are convenient for practical evaluations are obtained. The physical and mathematical model for force characteristics of a non-uniform electric field is developed. With a sufficiently small size of the interelectrode gap, the integral force effect of discretely distributed charges can be significantly higher than with a uniform distribution of the same charge. At reasonable surface charge densities, these phenomena are usually observed at interelectrode gaps less than tenths of a micrometer.
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Yao, Jun, Eldin Wee Chuan Lim, Chi Hwa Wang, and Ning Li. "Process Tomographic Measurements of Granular Flow in a Pneumatic Conveying System." Advanced Materials Research 508 (April 2012): 75–79. http://dx.doi.org/10.4028/www.scientific.net/amr.508.75.
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The application of process tomography (PT) technologies, i.e. Electrostatic Tomography (EST) and Electrical Capacitance Tomography (ECT) to investigate complex industrial processes has obtained wide popularity in recent years. This study focuses on the characterization of non-uniformly distributed electrostatic effects across the cross-section of a pneumatic transportpipe. A digital electrometer was used to measure the electrostatics current and an ECT was used to observe the particle distribution in a vertical pipe. Due to non-uniform particle-wall collisions, the electrostatics generated was observed to be non-uniformly distributed across the pipe cross-section, especially at pipe bends and in a vertical pipe. Large electrostatic effects were associated with high particle concentration in the pipe. There was a good correspondence between the electrostatic effects measured and particle concentration distributions obtained using ECT. Based on ECT measurements at the vertical pipe section, it was observed that particles tended to concentrate at sections where generation of electrostatic charges was high. Thus, it is clear that electrostatic effects should be the key factor giving rise to non-uniform particle concentration distribution in pneumatic transport lines.
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Khan, Aminul Islam, and Prashanta Dutta. "Analytical Solution of Time-Periodic Electroosmotic Flow through Cylindrical Microchannel with Non-Uniform Surface Potential." Micromachines 10, no. 8 (July 26, 2019): 498. http://dx.doi.org/10.3390/mi10080498.
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Time-periodic electroosmotic flow (EOF) with heterogeneous surface charges on channel walls can potentially be used to mix species or reagent molecules in microfluidic devices. Although significant research efforts have been placed to understand different aspects of EOF, its role in the mixing process is still poorly understood, especially for non-homogeneous surface charge cases. In this work, dynamic aspects of EOF in a cylindrical capillary are analyzed for heterogeneous surface charges. Closed form analytical solutions for time-periodic EOF are obtained by solving the Navier–Stokes equation. An analytical expression of induced pressure is also obtained from the velocity field solution. The results show that several vortices can be formed inside the microchannel with sinusoidal surface charge distribution. These vortices change their pattern and direction as the electric field change its strength and direction with time. In addition, the structure and strength of the vorticity depend on the frequency of the external electric field and the size of the channel. As the electric field frequency or channel diameter increases, vortices are shifted towards the channel surface and the perturbed flow region becomes smaller, which is not desired for effective mixing. Moreover, the number of vorticities depends on the periodicity of the surface charge.
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Blokhintsev, L. D., and D. A. Savin. "Study of the Influence of Different Methods of Taking into Account the Coulomb Interaction on Determining Asymptotic Normalization Coefficients within the Framework of Exactly Solvable Model." Physics of Atomic Nuclei 84, no. 4 (July 2021): 401–7. http://dx.doi.org/10.1134/s1063778821040098.
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Abstract It is shown that the Schrödinger equation for the sum of the potential of a square well and the Coulomb potential of a uniformly charged sphere admits an analytical solution for arbitrary values of the orbital angular momentum. An explicit form of this solution has been found. Using the obtained solution, the influence of the Coulomb interaction for both point and distributed nuclear charges on the values of asymptotic normalization coefficients for various nuclear systems is investigated. It is shown that taking into account the non-point distribution of the nuclear charge has little effect on the calculated values of the asymptotic normalization coefficients, provided that the binding energy of the system is assumed to be fixed.
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Bakke, Knut, and Claudio Furtado. "Analysis of the interaction of an electron with radial electric fields in the presence of a disclination." International Journal of Geometric Methods in Modern Physics 16, no. 11 (November 2019): 1950172. http://dx.doi.org/10.1142/s021988781950172x.
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We consider an elastic medium with a disclination and investigate the topological effects on the interaction of a spinless electron with radial electric fields through the WKB (Wentzel, Kramers, Brillouin) approximation. We show how the centrifugal term of the radial equation must be modified due to the influence of the topological defect in order that the WKB approximation can be valid. Then, we search for bound states solutions from the interaction of a spinless electron with the electric field produced by this linear distribution of electric charges. In addition, we search for bound states solutions from the interaction of a spinless electron with radial electric field produced by uniform electric charge distribution inside a long non-conductor cylinder.
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Ye, Hui, and Austen Curcuru. "Deformation but not migration and rotation – a model study on vesicle biomechanics in a uniform DC electric field." Journal of Biomedical Engineering and Informatics 3, no. 1 (October 13, 2016): 18. http://dx.doi.org/10.5430/jbei.v3n1p18.
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Background: Biological cells migrate, deform and rotate in various types of electric fields, which have significant impact on the normal cellular physiology. To investigate electrically-induced deformation, researchers have used artificial giant vesicles that mimic the phospholipid bilayer cell membrane. Containing primarily the neutral molecule phosphatidylcholine, these vesicles deformed under evenly distributed, strong direct current (DC) electric fields. Interestingly, they did not migrate or rotate. A biophysical mechanism underlying the kinematic differences between the biological cells and the vesicles under electric stimulation has not been worked out. Methods: We modeled the vesicle as a leaky, dielectric sphere and computed the surface pressure, rotation torques and translation forces applied on the vesicle by a DC electric field. We compared these measurements with those in a biological cell that contains non-zero, intrinsic charges (carried by the functional groups on the membrane). Results: For both the vesicle and the cell, the electrically-induced charges interacted with the local electric field to generate radial pressure for deformation. However, due to the symmetrical distribution of both the charges and the electric field on the vesicle/cell surface, the electric field could not generate net translation force or rotational torques. For a biological cell, the intrinsic charges carried by the cell membrane could account for its migration and rotation in a DC electric field. Conclusions: Results from this work suggests an interesting control diagram of cellular kinematics and movements by the electric field: cell deformation and migration can be manipulated by directly targeting different charged groups on the membrane. Fate of the cell in an electric field depends not only on the delicately controlled field parameters, but also on the biological properties of the cell.
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Qie, X., S. Soula, and S. Chauzy. "Influence of ion attachment on the vertical distribution of the electric field and charge density below a thunderstorm." Annales Geophysicae 12, no. 12 (December 31, 1994): 1218–28. http://dx.doi.org/10.1007/s00585-994-1218-6.
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Abstract. A numerical model called PICASSO [Production d'Ions Corona Au Sol Sous Orage (French) and Production of Corona Ions at the Ground Beneath Thundercloud (English)], previously designed, is used to describe the evolution of the principal electrical parameters below a thunderstorm, taking into account the major part played by corona ions. In order to improve the model restitution of a real situation, various improvements are performed: an initial vertical distribution of aerosol particles is introduced instead of the previously used uniform concentration; time and space calculation steps are adjusted according to the electric field variation rate; the upper boundary condition is improved; and the coefficients of ion attachment are reconsidered with an exhaustive bibliographic study. The influence of the ion attachment on aerosol particles, on the electric field and charge density aloft, is studied by using three different initial aerosol particle concentrations at ground level and two types of initial vertical distributions: uniform and non-uniform. The comparison between field data and model results leads to adjust the initial aerosol particle concentration over the experimental site at the value of 5000 cm-3 which appears to be highly realistic. The evolutions of the electric field and of the charge density at altitude are greatly influenced by the aerosol concentration. On the contrary, the surface intrinsic field, defined as the electric field that would exist underneath a thundercloud if there were no local charges, is weakly affected when the model is forced by the surface field. A good correlation appears between the success in the triggered lightning attempts and this intrinsic field evaluation. Therefore, when only the surface field is available, the model can be used in a triggered lightning experiment.
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Oularé, Sékouba, Alexis Kassi Kouamé, Mahaman Bachir Saley, Gabriel Etienne Ake, Michel Amani Kouassi, Gnangui Christian Adon, Fernand Koffi Kouamé, and René Therrien. "Estimation de la conductivité hydraulique des zones discrètes de réseaux de fractures à partir des charges hydrauliques : application au bassin versant du N’zo (ouest de la Côte d’Ivoire)." Revue des sciences de l’eau 29, no. 3 (February 13, 2017): 279–301. http://dx.doi.org/10.7202/1038928ar.
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L’estimation de la conductivité hydraulique d’un aquifère de socle à l’échelle régionale demeure un défi majeur. À cette échelle, les données sont rares, en quantité et en qualité. Cette étude propose une approche d’estimation de la conductivité hydraulique des aquifères de socle à partir de la calibration d’un modèle d’écoulement au moyen des charges hydrauliques. Elle est appliquée au bassin du N’zo couvrant une superficie de 4 300 km2. La méthodologie adoptée fait l’hypothèse que la perméabilité de l’aquifère est liée à des fractures verticales, perméables sur 100 m à partir de la surface. Elle fait aussi l’hypothèse que ces fractures peuvent être identifiées sous forme de linéaments et que tous les linéaments sont des fractures et sont perméables. La première étape de cette méthodologie est la cartographie des zones discrètes de perméabilité de l’aquifère. Elles sont identifiées à partir de l’analyse de la densité et l’orientation des « fractures » à l’échelle de mailles de travail. Les fractures sont assimilées aux linéaments cartographiés à partir d’une image radar. Six configurations spatiales de zones discrètes de perméabilité sont générées avec des mailles carrées de 2 à 12 km de côté. La deuxième étape porte sur la construction du modèle numérique d’écoulement à partir des limites extérieures du bassin versant, du MNT (Modèle numérique de terrain), du réseau hydrographique et d’une recharge uniforme. Enfin, la troisième étape consiste à transférer chaque configuration de zones discrètes de perméabilité générée au sein du modèle numérique d’écoulement, puis à le calibrer en régime permanent au moyen de charges hydrauliques observées ponctuellement (86 points de mesure). Les résultats indiquent que le modèle optimal de distribution spatiale des zones discrètes de perméabilité est obtenu avec les mailles de 4 km de côté. Les conductivités hydrauliques calculées oscillent entre 1,1 x 10-6 et 2,4 x 10-5 m∙s-1. Cependant, ces valeurs doivent être prises avec précaution, car l’identification des zones homogènes du réseau de fractures est basée sur l’approche très controversée des linéaments et la calibration est effectuée seulement avec des charges hydrauliques et non avec des flux. Le modèle conceptuel ainsi élaboré pourrait être amélioré en caractérisant l’hétérogénéité de l’aquifère de socle à partir d’autres hypothèses telles que la lithologie et par l’introduction d’autres types de données dans la calibration (ex. : débits, carte piézométrique).
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Luts, A. R., A. P. Amosov, E. I. Latukhin, A. D. Rybakov, V. A. Novikov, and S. I. Shipilov. "Self-propagating high-temperature synthesis of (Al–2%Mn)–10%TiC and (Al–5%Cu–2%Mn)–10%TiC nanostructured composite alloys when doped with manganese powder." Izvestiya Vuzov. Poroshkovaya Metallurgiya i Funktsional’nye Pokrytiya (Universitiesʹ Proceedings. Powder Metallurgy аnd Functional Coatings), no. 3 (September 16, 2018): 30–40. http://dx.doi.org/10.17073/1997-308x-2018-3-30-40.
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The paper studies the effect of doping with manganese powder on the production of (Al–2%Mn)–10%TiC and (Al–5%Cu– 2%Mn)–10%TiC nanostructured composite alloys by self-propagating high-temperature synthesis (SHS) of TiC titanium carbide nanoparticles from Ti + C charge in the melt of matrix alloys. First, manganese metal powder was added to the matrix bases of Al and Al–5%Cu composite alloys in the amount of 2 wt%. This improved aluminum base tensile strength from 81 MPa (for the original A7 grade aluminum) to 136 MPa and aluminum-copper base tensile strength to 169 MPa. It was found that when aluminum was doped with manganese only, the SHS reaction proceeded weakly and not completely, and the carbide phase size in the resulting alloy (Al–2%Mn)–10%TiC varied from nanoscale to several micrometers. When 10% Na2TiF6halide salt was added to the SHS charge, the SHS process intensified, but the resulting alloy contained a considerable amount of pores, inclusions of unreacted charge and large agglomerates of TiC ceramic nanosized particles. Similar results were obtained in cases of using Ti + C and Ti + C + 10%Na2TiF6SHS charges, but with joint doping of matrix aluminum with copper and manganese, providing more uniform distribution of the TiC nanodispersed phase. The best results were obtained by reducing the Na2TiF6salt additive to 5 % of the SHS charge mass, which facilitated smoother and complete synthesis of predominantly TiC nanosized particles and the formation of a non-porous uniform microstructure of (Al–5%Cu–2%Mn)–10%TiC composite alloy with an ultimate tensile strength of 213 MPa and 6,6 % elongation.
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Ghosal, Sandip, and John D. Sherwood. "Screened Coulomb interactions with non-uniform surface charge." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, no. 2199 (March 2017): 20160906. http://dx.doi.org/10.1098/rspa.2016.0906.
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The screened Coulomb interaction between a pair of infinite parallel planes with spatially varying surface charge is considered in the limit of small electrical potentials for arbitrary Debye lengths. A simple expression for the disjoining pressure is derived in terms of a two-dimensional integral in Fourier space. The integral is evaluated for periodic and random charge distributions and the disjoining pressure is expressed as a sum over Fourier–Bloch reciprocal lattice vectors or in terms of an integral involving the autocorrelation function, respectively. The force between planes with a finite area of uniform charge, a model for the DLVO interaction between finite surfaces, is also calculated. It is shown that the overspill of the charge cloud beyond the region immediately between the charged areas results in a reduction of the disjoining pressure, as reported by us recently in the long Debye length limit for planes of finite width.
Dissertations / Theses on the topic "Distribution de charges non uniforme"
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Derot, Claire. "Interactions électrostatiques entre colloïdes non uniformément chargés." Montpellier 2, 2009. http://www.theses.fr/2009MON20211.
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Nous avons étudié les interactions entre colloïdes chargés dont la distribution de charge n'est pas uniforme. Pour faire varier la distribution de charge, nous avons utilisé un système neutre bien connu que nous avons dopé progressivement par des tensioactifs cationiques. Ainsi, la distribution de charge a pu être modulée en jouant sur le taux de dopage moyen, la valence des tensioactifs et la structure de leur tête polaire. Nous avons mis en évidence les interactions répulsives entre ces colloïdes par diffusion de rayonnement et constaté l'influence de la distribution de charges : plus le caractère discret des charges est marqué, moins les particules se repoussent. En tenant compte de la condensation des contre ions, nous avons montré que le potentiel d'interaction entre colloïdes non uniformément chargés était de la même forme que celui qui décrit classiquement les interactions entre colloïdes chargés. Cependant, un écrantage supplémentaire doit être introduit. Il est déterminé par la distance entre charges à la surface des colloïdes et par la structure des tensioactifs utilisés comme dopants. La relaxation des fluctuations d'intensité diffusée a été étudiée par diffusion dynamique de la lumière. Deux modes diffusifs de relaxation ont été mis en évidence ainsi qu'un troisième mode lié à la vitesse d'échange des dopants entre les particules colloïdales. Nous avons montré que les amplitudes relatives des deux modes diffusifs étaient directement reliées à la variation du taux de dopage d'une goutte à l'autre (polydispersité en charge) et à l'intensité des interactions. Ainsi, la contribution du mode d'auto-diffusion est d'autant plus importante que la polydispersité en charge est élevée et que les interactions répulsives sont fortesWe investigated interactions between charged colloids with a non uniform charge distribution. We used a neutral and well known system, on which we added cationic surfactants to vary the charge distribution. Thus, charge distribution change with the mean doping rate, the surfactant valency and the polar head structure. We underlined repulsive interactions between colloids by rays scattering and we noticed the charge distribution impact: the more the charges are discrete, the less particles repel each other. By taking account of counter ions condensation, we showed that the interaction potential between non-uniformly charged colloids was the same as the classical interaction potential between charged colloids. Nevertheless, an extra screening has to be introduced. It is determined by the distance between surface charges and by ionic surfactant structure. The relaxation of scattering intensity fluctuations was studied by dynamic light scattering. Two diffusive relaxation modes were underlined. A third mode appeared and it is connected with the rate of surfactant exchange between colloidal particles. We showed that relative amplitudes of the two diffusive modes were connected with the variation of doping rate between droplets (charge polydispersity) and the interactions intensity. Thus, the contribution of the self diffusion mode is all the more important as charge polydispersity is high and repulsive interactions are strong
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Provillard, Julien. "Automates cellulaires non-uniformes." Nice, 2012. http://www.theses.fr/2012NICE4082.
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Les automates cellulaires (CA) sont des systèmes dynamiques discrets très utilisés dans de nombreux domaines scientifiques. Leurs principales caractéristiques sont d’agir de manière locale, synchrone et uniforme sur l’ensemble des cellules d’une grille régulière. Ces systèmes produisent une grande variété de dynamiques et ont été largement étudiés dans la littérature. De nombreuses variantes ont été proposées. Dans ce travail de thèse nous nous intéresserons aux automates cellulaires non-uniformes (nu-CA). Il s’agit, essentiellement, d’automates cellulaires dans lesquels la contrainte d’uniformité a été relâchée. Dans un premier temps, nous considérerons une famille de nu-CA qui permet de représenter des perturbations dans la structure d’un CA. Il s’agit d’étudier l’influence d’une panne ou d’une erreur ponctuelle dans l’implémentation d’un CA et notamment son influence sur la dynamique. Nous verrons que de nombreuses propriétés ne sont pas stables (à l’exception notable de l’équicontinuité) mais que l’on peut alors établir des liens entre un CA et ses modèles de perturbation. Dans une seconde partie, nous cherchons à déterminer les propriétés que peut avoir un nu6CA en fonction des comportements locaux que l’on peut observer. On se donne un ensemble de règles locales qui peuvent intervenir dans un nu-CA et nous nous intéressons à la façon d’agencer ces règles pour produire certaines propriétés dans l’automate induit. Nous associons alors, à chacune de ces propriétés, un langage de distributions que nous caractérisons) à l’aide de la théorie des langagesCellular automata (CA) are discrete dynamical systems widely used in many scientific domains. Their main characteristic is to act locally, synchronously and uniformly on a regular set of elementary components called cells. These systems have a huge variety of dynamical behaviours and have been extensively studied in literature. Several variants have been proposed. In this work we are interested in non-uniform cellular automata (nu-CA). They are, essentially, CA in which the uniformity constraint has been relaxed. In the first part, we study a family of nu6CZA which allows to easily representing perturbations of the structure of a CA. The idea is to study the impact of the dynamics of failure or of an error in the physical implementation of a CA by electronic components. Indeed, we will prove that several dynamical properties are not structurally stable (except for the equicontinuity property). However, we will show how to link properties of a CA and its “perturbed” versions. In the second part, we try to infer the global properties of a nu-CA from the local behaviours we can observe. Given a set of local rules which can appear in a given nu-CA, we study the way of mowing them to obtain given global behaviours. Moreover, we associate global properties with peculiar formal languages and we completely characterize these formal languages. In this way we obtain a natural notion of complexity for properties on nu-CA. A property is a complex as the class of languages from which it is characterizes
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Talbi, Yacine. "Excitations magnétiques dans des films minces et des nanostructures présentant une distribution d'aimantation non uniforme." Paris 13, 2010. http://www.theses.fr/2010PA132026.
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Ce travail a porté sur l'analyse du comportement statique d'objets magnétiques sous forme de couches minces ou de plots submicrométriques présentant une distribution d'aimantation fortement non-uniforme et leurs excitations magnétiques. Dans ce but diverses techniques expérimentales ont été utilisées : la microscopie à force à magnétique (MFM), la résonance ferromagnétique de type micro-ruban (FMR) et la spectroscopie Brillouin (BLS). Dans une première étude, fortement expérimentale portant sur des films continus, la première étape a concerné la recherche des paramètres magnétiques et l'analyse fine de la distribution d'aimantation présente communément appelée « rubans faibles ». Un point important a consisté en la maîtrise de cette structure et notamment de sa périodicité lors des expériences dynamiques. Ce travail a été réalisé par une étude approfondie en MFM sous champ appliqué. Pour l'analyse des excitations magnétiques observées par FMR et BLS, deux modèles simples ont été proposés. Le premier utilisant une approche de Thiele afin rendre compte des déplacements de vortex tandis que le second permet d'expliquer les spectres d'ondes de spin observés. La seconde partie de notre recherche fut quant à elle purement numérique offrant une étude sur des petits plots permettant toutefois l'établissement d'une structure en vortex. Le code de calcul OOMMF fut utilisé à cet effet. Le comportement statique et dynamique a été analysé en fonction du champ appliqué et ce pour diverses tailles de plotsThis work has focused on the analyzis of the static behavior of magnetic objects (layers or dots) with a non-uniform distribution of magnetization. For this purpose various experimental techniques have been used: the magnetic force microscopy (MFM), ferromagnetic resonance type micro-strip (FMR) and Brillouin spectroscopy (BLS). In a first study, highly experimental on continuous films, the first step deals with the search of magnetic parameters and the detailed analysis of the distribution of magnetization present commonly called "low bands". An important point consisted of mastering this particular structure and its regularity in dynamic experiments. This work was carried out by a comprehensive study MFM under applied field. For the analysis of magnetic excitations observed by FMR and BLS, two simple models have been proposed. The first using a Thiele approach to account for displacement of vortices while the latter helps explain the spin wave spectra observed. The second part of our research was purely for its digital offering study on small plots, however, allowing the establishment of a vortex structure. The computer code was OOMMF used for this purpose. The static and dynamic behavior was analyzed as a function of applied field and for various sizes of dots
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Zhuang, Linqi. "Les effets de la répartition non-uniforme des fibres sur la propagation des fissures á l’interface fibre/matrice dans les matériaux composites." Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0321/document.
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Dans ces travaux, nous avons étudié numériquement la croissance du décollement de l'interface fibre / matrice d'un composite UD avec garnissage hexagonale de fibre sous charge longitudinal et transversal. Nous avons mis l'accent en particulier sur l'influence des fibres voisines sur sa croissance. Dans la présente étude, le taux de libération d'énergie (ERR) est considéré comme la force motrice de la croissance du décollement et a été calculé sur la base de Integral J et de la technique de fermeture virtuelle de fissures (VCCT) à l'aide du logiciel de calcul par éléments finis ANSYS. Dans la présente recherche de thèse, nous avons étudier d’abord l'influence des fibres voisines sur ERR d'une décohésion émanant d'une rupture de fibre en condition de chargement longitudinal. Dans le cas du chargement longitudinal, la croissance du décollement est gouvernée par le mode II. Comme point de départ l’étude, nous avons mis place un modèle axisymétrique composé de 5 cylindres concentriques représentant la fibre endommagée, la matrice environnante, les fibres voisines, la matrice environnante et le composite effectif généré. On constate qu'il y a deux stades de croissance, la première étape correspond à une longueur courte du décollement, l'ERR diminue à mesure que l'angle du décollement augmente, et la présence de voisins augmente significativement la décohésion de l'ERR. Pour une décohésion relativement longue, le décollement se situe dans une région de croissance en état stationnaire lorsque l'ERR est pratiquement constant quelle que soit la longueur du décollement. À l’état stationnaire de la croissance du défaut, la présence de fibres voisines n'a que peu d'effet sur l'ERR. Les travails ultérieurs, nous avons mis en place un modèle 3-D (explicite) avec la fibre endommagée et ses 6 fibres les plus proches dans un composite UD compacté hexagonal, entourées par le composite homogénéisé. Sur la base des résultats obtenus, nous avons montré que l'ERR varie le long de la face frontale et a son maximum à l'endroit circonférentiel où la distance entre deux centres de fibre est la plus petite. Cela indique que le front du décollement n’est pas circulaire. Pour l'état stable du décollement, la présence de fibres a peu d'effet sur l'ERR qui progresse le long du front du décollement. Pour un décollement court, la présence de fibres augmente l'ERRS moyenné, et cette augmentation est plus significative lorsque la distance entre fibre est la plus petite. Après l’étude du la décollement fibre / matrice en charge longitudinale, nous avons commencé à étudier la croissance du décollement fibre / matrice le long de la circonférence de la fibre sous charge transversale. On constate que la croissance de la du décollement est en mode mixte, et les composants ERR du mode I et du mode II augmentent avec l'augmentation de l'angle de déformation puis diminuent. La croissance du décollement démarre principalement en mode I pour les petits angles de décollement et se poursuit en mode II. La présence de fibres voisines a un effet d’accroissement sur la croissance du décollement jusqu'à certains petits angles et change ensuite en effet protecteur. En fin, nous avons étudié l'interaction entre deux décollement sous chargement transversale. Nous avons constaté que lorsque deux décollements sont proches l'un de l'autre, l'interaction entre devient beaucoup plus forte et conduit à l'augmentation significative de l'ERR de chaque décollement, ce qui facilite la croissance du décollementIn the presence thesis, the growth of fiber/matrix interface debond of a UD composite with hexagonal fiber packing under longitudinal and transverse tensile loading was investigated numerically, with the special focus on the influence of neighboring fibers on its growth. In the current study, energy release rate (ERR) is considered as the driving force for debond growth and was calculated based on J Integral and Virtual Crack Closure Technique (VCCT) using finite element software ANSYS. In the present thesis research, we started with investigating the influence of neighboring fibers on ERR of a debond emanating from a fiber break in longitudinal loading condition. In longitudinal loading case, debond growth is mode II dominated. As the starting point for the research, an axisymmetric model consisting 5 concentric cylinders that represent broken fiber with debond, surrounding matrix, neighboring fibers, surrounding matrix and effective composites was generated. It’s found that there are two stages of debond growth, the first stage is when debond length is short, the ERR decreases with increasing debond angle, and the presence of neighboring significantly increase the ERR of debond. For relatively long debond, the debond is in a steady state growth region when ERR is almost constant regardless of debond length. In steady state of debond growth, the presence of neighboring fibers have little effect on the ERR. In the later research, a 3-D model was generated with broken fiber and its 6 nearest fibers in a hexagonal packed UD composite were modelled explicitly, surrounded by the homogenized composite. Based on the obtained results, it’s shown that ERR is varying along debond front, and has its maximum at the circumferential location where the distance between two fiber center is the smallest. This indicates the debond front is not a circle. For steady state debond, the presence of fibers have little effect on ERR that averages along debond front. For short debond, the presence of fibers increases the averaged ERRS, and that the increase is more significant when inter-fiber distance are the smallest. When we conclude our investigation on fiber/matrix debonding under longitudinal loading, we began studying the growth of a fiber/matrix debond along fiber circumference under transverse loading. It’s found that debond growth is mixed-mode, and both mode I and mode II ERR components increase with increasing debond angle and then decreases. Debond growth is mode I dominated for small debond angle and then switch to mode II dominated. The presence of neighboring fibers have an enhancement effect on debond growth up to certain small debond angle and then changes to a protective effect. Finally, the interaction between two arc-size debond under transverse loading is investigated. It’s found that when two debonds are close to each other, the interaction between two debond becomes much stronger, and that interaction leads to the increase of ERR of each debond significantly, which facilitates further debond growth for both debond
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Maltoni, Matteo. "Energy emission by moving charges." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16347/.
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This paper analizes the power emitted by charges accelerated on general trajectories. The electric and magnetic field radiated are calculated in detail through the retarded potentials, and the non-relativistic, quasistatic and radiation regimes are treated. The radiated power is obtained through the calculation of the Poynting vector, and the two cases of linear and circular accelerators are analyzed. After this, the distribution in frequencies of this radiation is studied for a moving charge and a moving magnetic moment, and the intensity distribution in angles and frequencies is generalized to the case of a continuous set of charges in motion.
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Blum, Raphaël. "Etude de la distribution de charges électroniques au sein de verres isolants et son application au poling." Paris 11, 2006. http://www.theses.fr/2006PA112275.
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Les materiaux vitreux possedent une centrosymetrie macroscopique qui interdit les non-linearites optiques du second ordre. Untraitement de poling thermique, consistant a appliquer sous chauffage, un champ electrique, permet neanmoins de creer une susceptibilite non-lineaire d’ordre deux d’environ 1 pm/v. Ceci en raison du champ electrique interne genere au sein du materiau par la migration d’especes cationiques. Cette these porte sur l’etude de procedes alternatifs de poling, pour lesquels le champ electrique interne resulte de la migration d’especes electroniques (electrons et/ou trous). Dans un premier temps, nous abordons l’irradiation par faisceau d’electrons et la mesure du rendement d’emission secondaire. Nous discutons de l’influence de divers parametres experimentaux sur la valeur et l’evolution du rendement d’emission electronique secondaire et montrons que de telles mesures permettent d’evaluer le caractere isolant (ou “piegeur”) des verres etudies et ainsi de tester leur aptitude a conserver une charge d’espace induite par polingla suite de notre travail traite du poling par faisceau d’electrons et du poling par rayons x. Nous y detaillons nos travaux visant a l’optimisation des differents parametres d’irradiation et leur effet sur les performances optiques atteintes. Enfin, nous jetons les bases d’une modelisation de la charge d’espace induite lors d’une irradiation par faisceau d’electrons ou par rayons x. Ce modele, une fois complet, nous permettra une meilleure interpretation des courbes de rendements d’emissions electroniques secondaires ainsi qu’une optimisation des conditions de poling par les deux procedes etudiesVitreous materials have a macroscopic centrosymetry that prohibits second-order optical non-linearities. A thermal poling treatment i. E. Applying an electric field under heating, makes it possible nevertheless to create a second-order non-linear susceptibility of about 1 pm/v. This was explain by the creation of an internal electric field due to cationic species migration. This thesis deals with alternative poling processes, for which the internal electric field results from the migration of electronic species (electrons and/or holes). We, firstly, describe the effect of an e-beam irradiation an a sample and the measurement of the secondary electron emission yield (seey). We discuss the influence of various experimental parameters on the value and the evolution of seey and show that such a measurements is a usefull tool to evaluate the insulating properties of various glasses and thus test their ability to store a poling induced space charge. Then, we explain the basis of e-beam and x-ray poling and detail our work on the optimization of the various irradiation parameters and their effect on the non-linear optical properties. Finally, we report our attempt to modelize the space charge induced during an e-beam or x-ray irradiation model, once completed, such a model, could give us a better understanding of the seey curves as well as the optimized poling conditions
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Mercier, Aurélien. "Pilotage de la production décentralisée et des charges non conventionnelles dans le contexte Smart Grid et simulation hybride temps réel." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAT078/document.
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Dans le domaine des réseaux de distribution d'électricité, l'ouverture du marché de l'énergie à la concurrence et l'insertion massive des génératrices décentralisées d'énergie de ces dernières années conduisent à une profonde modification du fonctionnement et de l'exploitation des réseaux. Dans ce contexte, des solutions de pilotage de la consommation et de la production doivent être apportées, afin de permettre au réseau actuel d'accueillir les nouvelles unités de production et les charges de demain, telles que les panneaux photovoltaïques, les micro-éoliennes, la cogénération, les véhicules électriques, les maisons intelligentes, etc. Ces pilotages permettent d'influencer la consommation et la production instantanées des utilisateurs du réseau. Ainsi, il devient possible d'agir sur la consommation de façon à lisser les pics ou synchroniser la demande aux périodes de forte production des énergies renouvelables. De la même façon, la production peut être pilotée pour participer aux services systèmes. Ces stratégies de pilotage, basées sur l'utilisation des nouvelles technologies de l'information et de la communication, ont pour objectifs d'éviter une dégradation de la qualité de l'onde de tension et une reconstruction complète du réseau de distribution, qui serait économiquement très couteuse. Ces travaux, intégrés au projet GreenLys, financé par l'agence française de l'environnement et de la maitrise de l'énergie, évaluent l'impact des génératrices décentralisées d'énergie et des véhicules électriques sur le réseau de distribution, puis développent des solutions de pilotage. Deux types de pilotage sont étudiés : le pilotage de la phase de raccordement d'une installation monophasée, puis le pilotage de la puissance réactive des génératrices décentralisées d'énergie. Ces pilotages sont développés en s'appuyant sur les nouveaux composants des réseaux électriques de demain, comme les compteurs intelligents. Dans une dernière partie, les stratégies de pilotage développées sont évaluées sur des équipements réels à partir d'une plateforme de simulation hybride temps réelIn the electricity distribution network field, because of the electricity market opening and the large-scale insertion of dispersed generators (DJ) in these last years, the network undergoes radical modification in both operation and exploitation. In this context, some new integration solutions are invented in order to be able to connect the DJ, as photo-voltaic panels, micro wind turbines, cogeneration units, etc, and the new loads, as electric vehicles and smart home, without reduce the voltage wave quality or involve a very expensive power systems reinforcement. The objectives of those solutions are to influence the consumer consumption in order to reduce the peak consumption level and shift the consumption on the high renewable production period, and control the DJ output to participate to the service system. The new information and communication technologies (NICT) are strongly used in the development of those control strategies. This PhD work is including in the French project GreenLys supported by the French environment and energy management agency. GreenLys is a 4 years project focus on the development of a real scale Smart Grid in the two French cities Lyon and Grenoble. As a first step, this work evaluating the impact of the DJ and the electric vehicle on the distribution network. From the result of this impact study, two types of decentralized control strategies are investigated. The first one is focus on the phase connection. Since the majority of consumers and DJ connected on the distribution grid are single phases, methods allowing to choose the best phase connection are study. The second one is focus on new DJ reactive power control strategies. In the last part, the strategies are evaluated on a Power Hardware In the Loop simulation and real solar inverter
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Dagher, Gulnar. "Mesure directe et non destructive de la distribution de charges d'espace à l'échelle nanométrique dans les isolants et les semi-conducteurs : application à la microélectronique." Paris 6, 2008. http://www.theses.fr/2008PA066573.
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Les isolants et les semi-conducteurs sont les principaux constituants des circuits intégrés, dont les performances croissantes sont notamment dus à la miniaturisation des composants, mais au prix d’une plus grande vulnérabilité : un champ électrique élevé favorise l’accumulation de charges, modifiant les caractéristiques du composant. Au contraire, les charges introduites par dopage contribuent à son bon fonctionnement. Pour une connaissance précise du profil de charges dans les isolants et les semi-conducteurs, un instrument de mesure directe et non destructive à l’échelle nanométrique est alors étudié dans ce mémoire. Une implémentation fondée sur une méthode pompe-sonde utilisant un laser femtoseconde permet d’obtenir une résolution spatiale inférieure à 50 nm. Une détection interférométrique ou électro-optique et l’accumulation d’un grand nombre de mesures sont nécessaires pour améliorer les signaux. Des mesures valident les premières étapes de la réalisation expérimentale.
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Ali, Zazou Abdelkrim. "Conception d'un outil d'optimisation dynamique du schéma d'exploitation du réseau de distribution d'électricité de SRD." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2017. http://www.theses.fr/2017ESMA0010.
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Le réseau de distribution électrique français, construit dans une optique de desserte d'électricité depuis les centrales de production en amont, vers les consommateurs en aval, est aujourd'hui le lieu de transits d'énergie multi-sens et dont la charge instantanée dépend à la fois des consommations et des productions locales. Il faut donc moderniser les modèles d'exploitation des réseaux actuellement utilisés.C'est dans ce contexte que le gestionnaire du réseau de distribution de la Vienne SRD, et les différentes équipes du laboratoire LIAS, ont cherché à mettre en place un outil d'optimisation des schémas d'exploitation des réseaux de distribution d'électricité de la VIENNE.Dans cette thèse, le trnvt1il s'est porté principalement sur la modélisation du problème et non sur les méthodes de résolution. En effet, le contexte industriel du développement de l'outil d'optimisation du réseau a permis de se rapprocher au mieux de la réalité des informations disponibles concernant le réseau électrique. Et il est apparu plus pertinent d'utiliser des méthodes de résolution exactes tout en recherchant à simplifier le modèle complexe de représentation du réseau électrique. Ainsi,un modèle simple d'optimisation basé sur le problème de Bot à coût minimum a été mis en place et une étude comparative a été réalisée avec les modèles complexes présents dans la littérature.Ce premier modèle a été reformulé et rendu convexe et quadratique, et permet ainsi d'obtenir des performances supérieures en terme de temps de résolution à solution égale. Le problème d'optimisation simplifié a aussi été élaboré pour permettre de prendre en compte un horizon de temps dans l'optimisation du réseau électrique', afin de prendre en compte des profils de consommation et de production au cours du temps. En effet, ceci permet ainsi de prendre en compte des variations liées au comportement des consommateurs et des producteurs reliés au réseau.Et pour finir. ces modèles d'optimisation ayant pour objectif d'être inséré dans un outil d'aide à la décision pour une utilisation dans un contexte industriel. différentes contraintes liées à l'exploitation des réseaux électriques ont été insérées au modèle.Différents cas d'études issus de la littérature sont présentés pour valider la pertinence du modèle au regard des méthodes existantes. Nous avons pu expérimenter en simulation notre optimisation de réseau sur données de réseaux réels, ce qui a démontré l'applicabilité de la démarche à des problèmes de tailles importantes correspondant à la réalité du réseau électrique de SRDThe French electrical distribution network was originally built to bring electricity from very large producers to consumers, but it has now become a place of multi-directional energy flows that rely on local production and consumption. Because of this new situation, the way of operating electrical networks needs to be renewed. In light of this, the local Distribution System Operator (SRO) of the French department Vienne and the different teams of the LIAS laboratory have worked together on the development of a distribution network configuration optimization tool. In this thesis the majority of the work was focused on the modeling part of the problem rather than on the development of new optimization methods. The industrial root of this project gave the opportunity to be very close to the reality of the available network data. Based on those observations,it was more consistent to use exact and precise optimization methods to solved simplified versions of the complex electrical network models.Thus a simple optimization model based on the minimum cost flow problem was developed, and a comparative study between the developed model and state of the art more complex one was led. This simple model was reformulated to become convex and quadratic and to reach better resolution time performances with the same solutions. This optimization problem was developed to take into account a time horizon factor into the optimization of the operation planning of the distribution network. The time horizon factor aim to represent the production and consumption variation over a selected period. Finally. because this model has to be integrated into a decision making helping tool that will be used by the DSO SRD several operational constraints were added into the optimization model. Several state of the art case studies arc presented to validate the model accuracy regarding existing methods. Simulation experiments were done on real networks data to show the applicability of the proposed optimization model over large scale case studies which correspond to the DSO SRO reality
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Grismayer, Thomas. "Etude théorique et numérique de l'expansion d'un plasma crée par laser : accélération d'ions à haute énergie." Phd thesis, Ecole Polytechnique X, 2006. http://pastel.archives-ouvertes.fr/pastel-00002924.
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Cette thèse constitue une étude théorique et numérique sur l'accélération d'ions à haute énergie dans l'expansion d'un plasma créé par laser. Les faisceaux d'ions émis en face arrière d'une cible irradiée présentent des caractéristiques (laminarité, faible divergence, largeur des spectres) qui les distinguent de ceux provenant de la face avant. Ces caractéristiques ouvrent la voie à de nombreuses applications telles que la protonthérapie ou la radiographie de protons. L'accélération des ions s'effectue via un champ électrostatique auto-consistant résultant de la séparation de charges entre les ions et les électrons chauds. La première partie du mémoire présente le modèle théorique fluide ainsi que le code de simulation hybride décrivant l'expansion du plasma. La modélisation numérique d'une récente expérience de sondage du champ d'expansion par faisceaux de protons permet de valider le modèle exposé. L'influence d'un gradient initial de densité sur l'efficacité de l'accélération est abordée dans le seconde partie. Nous établissons un modèle qui retrace la dynamique du plasma et plus particulièrement le déferlement du flot ionique. Les réseaux de courbes qui prévoient une nette dégradation de l'énergie maximale des protons pour de grandes longueurs de gradient sont en accord avec les résultats expérimentaux. L'hypothèse d'un équilibre de Boltzmann électronique, supposé dans le modèle guide, est remise en cause dans la troisième partie où les électrons suivent une description cinétique. La nouvelle version du code permet d'évaluer l'écart à la loi de Boltzmann, qui ne modifie pas cependant de manière significative l'énergie maximale acquise par les ions.
Book chapters on the topic "Distribution de charges non uniforme"
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Manton, Nicholas, and Nicholas Mee. "Fields—Maxwell’s Equations." In The Physical World. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198795933.003.0004.
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Chapter 3 explores the concept of the field, which is necessary to describe forces without resorting to action at a distance, and uses it to describe electromagnetism, as encapsulated by the Maxwell equations. First, scalar fields and the Klein–Gordon equation are discussed. Vector calculus is introduced. The physical meaning of Maxwell’s equations is explained. The equations are then solved for electrostatic fields. Non-uniform charge distributions and dipole moments are discussed. The vector and scalar potentials are introduced. Electromagnetic wave solutions of Maxwell’s equations are found and the Hertz experiment is described. Magnetostatics is discussed briefly. The Lorentz force is described and used to determine the motion of a charged particle in a cyclotron or synchrotron. The action principle for electromagnetism is described. The energy and momentum carried by the electromagnetic field are calculated. The reaction of a charged particle to its own electromagnetic field is considered.
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"Surface Charge Property of SiR/SiC Composites with Field-Dependent Conductivity." In Electrical Insulation Breakdown and Its Theory, Process, and Prevention, 219–54. IGI Global, 2020. http://dx.doi.org/10.4018/978-1-5225-8885-6.ch008.
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An electrical field distorted by the complicated cable accessory structure and non-uniform temperature distribution is a significant threat to high voltage direct current (HVDC) cable. Thus, the field grading material (FGM) with nonlinear conductivity can uniform local field receives attention. This chapter focuses on the surface charge property of SiR/SiC composites effected by temperature. Field strength and SiC content have a positive effect on the increase in conductivity. When the temperature increases, the threshold field decreases. At high SiC content, this phenomenon is more obvious. The influence of temperature is considered under DC voltage and impulse superimposed DC voltage.
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Osterlind, Steven J. "Rare Events." In The Error of Truth, 181–202. Oxford University Press, 2019. http://dx.doi.org/10.1093/oso/9780198831600.003.0011.
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This chapter shows that the quantification worldview was not spreading uniformly across even the developed world. In the United States, the spread was slow, because nearly everyone was consumed with making a new country. It was also slow in Russia, because of the dominance of the Romanoff family and their wars, and it did not spread to the Middle East, because it was preoccupied with warring and had almost no widespread education system. In England, an engineer named Charles Babbage contributed to bringing a mindset of quantification to ordinary people, through his Difference Engines Nos. 1 and 2, possibly the first programmable computers with CPUs. In probability theory, statistical “rare events” are described, and how Siméon Poisson made them into a specialized distribution is explained simply, as is his Poisson distribution, illustrated by the famous example of Prussian horse kicks. Further advancements included the invention of Fourier transforms.
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Coppens, Philip. "The Effect of Thermal Vibrations on the Intensities of the Diffracted Beams." In X-Ray Charge Densities and Chemical Bonding. Oxford University Press, 1997. http://dx.doi.org/10.1093/oso/9780195098235.003.0004.
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The atoms in a crystal are vibrating with amplitudes determined by the force constants of the crystal’s normal modes. This motion can never be frozen out because of the persistence of zero-point motion, and it has important consequences for the scattering intensities. Since X-ray scattering (and, to a lesser extent, neutron scattering) is a very fast process, taking place on a time scale of 10−18 s, the photon-matter interaction time is much shorter than the period of a lattice vibration, which is of the order Thus, the recorded X-ray scattering pattern is the sum over the scattering of a large number of 1/v, or ≈10−13s. instantaneous states of the crystal. To an extremely good approximation, the scattering averaged over the instantaneous distributions is equivalent to the scattering of the time-averaged distribution of the scattering matter (Stewart and Feil 1980). The structure factor expression for coherent elastic Bragg scattering of X-rays may therefore be written in terms 〈ρ(r)〉, of the thermally averaged electron density: . . . F(H)=∫unit cell〈ρ(r)〉 exp (2πi H ·r) dr (2.1) . . . The smearing of the electron density due to thermal vibrations reduces the intensity of the diffracted beams, except in the forward |S| = 0 direction, for which all electrons scatter in phase, independent of their distribution. The reduction of the intensity of the Bragg peaks can be understood in terms of the diffraction pattern of a more diffuse electron distribution being more compact, due to the inverse relation between crystal and scattering space, discussed in chapter 1. The reduction in intensity due to thermal motion is accompanied by an increase in the incoherent elastic scattering, ensuring conservation of energy. In this respect, thermal motion is much like disorder, with the Bragg intensities representing the average distribution, and the deviations from the average appearing as a continuous, though not uniform, background, generally referred to as thermal diffuse scattering or TDS. A crystal with n atoms per unit cell has 3nN degrees of freedom, N being the number of unit cells in the crystal.
Conference papers on the topic "Distribution de charges non uniforme"
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SANCHEZ, Martin. "Distribution transitoire des matières en suspension dans un écoulement unidirectionnel non uniforme." In Conférence Méditerranéenne Côtière et Maritime - Coastal and Maritime Mediterranean Conference. Editions Paralia, 2015. http://dx.doi.org/10.5150/cmcm.2015.016.
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Roshandel, R. "Modeling, Design and Fabrication of Non-Uniform Catalyst Layers for PEM Fuel Cells." In ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2010. http://dx.doi.org/10.1115/fuelcell2010-33261.
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Catalyst layers are one of the most important parts of the PEM fuel cells and the cell performance is highly related to its structure. Catalyst layers are generally made by uniform distribution of catalyst on carbon cloth or carbon papers to form electrodes. In this paper, the idea of using non-uniform catalyst layer instead of common uniform catalyst layers is presented and simulated by a two-dimensional steady-state computational model. The model accounts for species transport, electrochemical kinetics, charge transport and current density distribution. A fuel cell test stand is designed and built to facilitate experimental validation of the model. Modeling results show that electrical current in catalyst layer is non-uniform, influenced by the channel-land patterns in bipolar plate geometry. Our simulations results also suggest that some non-uniform catalyst distribution patterns regarding to bipolar plate configuration will improve the performance of the whole catalyst layer by increasing catalyst utilization factor. Therefore, it is necessary to design non-uniform catalyst layers regarding to specific procedure. Plasma sputtering method is used to fabricate non-uniform catalyst layers. In this method, the platinum is deposited on the carbon cloth in the plasma-processing chamber. Indeed, an experimental procedure is presented to facilitate the fabrication of non-uniform catalyst layers by plasma sputtering.
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Shi, Junxiang, and Xingjian Xue. "Bi-Functionally Graded Electrode Supported SOFC Modeling and Computational Thermal Fluid Analysis for Experimental Design." In ASME 2010 8th International Conference on Fuel Cell Science, Engineering and Technology. ASMEDC, 2010. http://dx.doi.org/10.1115/fuelcell2010-33099.
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A comprehensive 3D CFD model is developed for a bi-electrode supported cell (BSC) SOFC. The model includes complicated transport phenomena of mass/heat transfer, charge (electron and ion) migration, and electrochemical reaction. The uniqueness of the modeling study is that functionally graded porous electrode property is taken into account, including not only linear but nonlinear porosity distributions. Extensive numerical analysis is performed to elucidate the effects of both porous microstructure distributions and operating condition on cell performance. Results indicate that cell performance is strongly dependent on both operating conditions and porous microstructure distributions of electrodes. Using the proposed fuel/gas feeding design, the uniform hydrogen distribution within porous anode is achieved; the oxygen distribution within the cathode is dependent on porous microstructure distributions as well as pressure loss conditions. Simulation results show that fairly uniform temperature distribution can be obtained with the proposed fuel/gas feeding design. The modeling results can be employed to guide experimental design of BSC test and provide pre-experimental analysis, as a result, to circumvent high cost associated with try-and-error experimental design and setup.
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Wen, Jing Heng, and Michael J. Neely. "Optimization of Heat-Sink Fin Features by FEA Simulation." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-63529.
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Heat sinks are frequently used when heat exchange is required for electric circuits. In cases where the heat generation is evenly distributed, the height and spacing of fins are uniform. However, when heat generation is locally concentrated, uniform fin distribution is not the most efficient design. The original battery-charger heat-sink for a particular model of electric golf car featured a uniform fin design that had been in use for a long time. When re-tooling was required, the design team decided to investigate the heat-sink design for potential improvement. The project began by analyzing the heat-flow distribution of the baseline design. It was found that approximately 70% of the total heat flow was concentrated at a local area. The efficiency of the heat sink was based on material thermal property, fin height, fin spacing and etc. ANSYS thermal and structure were used to optimize these features. In order to understand how fin height and spacing influenced heat exchange, a three-step optimization process was used, including fin spacing optimization, fin height optimization and a combining analysis. The working environment was assumed to be non-forced convective cooling. The final design featured a highly non-uniform fin distribution that improved heat exchange by approximately 10% with a material reduction of about 15% compared with the baseline design. A US patent is pending for the improved heat-sink design.
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Huang, Jing, Hafez Bahrami, and Amir Faghri. "Analysis of a Permselective Membrane-Free Alkaline Direct Ethanol Fuel Cell." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-64988.
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A physical model is developed to study the coupled mass and charge transport in a permselective membrane-free alkaline direct ethanol fuel cell. This type of fuel cell is not only free of expensive ion exchange membranes and platinum based catalysts, but also features a facile oxygen reduction reaction due to the presence of alkaline electrolyte. The proposed model is first validated by comparing its predictions to the experimental results from literature and then used to predict the overall performance of the cell and reveal the details of ion transport, distribution of electrolyte potential and current density. It is found that: (i) KOH concentration lower than 1 M notably impairs cell performance due to low electrolyte conductivity; (ii) the concentration gradient and electrical field are equally important in driving ion transport in the electrolyte; (iii) the current density distributions in the anode and cathode catalyst layers keep non-uniform due to different reasons. In the anode, it is caused by the ethanol concentration gradient, while in the cathode it is because of the electrolyte potential gradient; and (iv) at low cell voltage, current density distribution in the catalyst layer shows stronger non-linearity in the anode than in the cathode.
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Wu, Zhemin, and Dongqing Li. "Mixing Enhancement by Induced-Charge Electrokinetic Flow." In ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer. ASMEDC, 2008. http://dx.doi.org/10.1115/mnht2008-52001.
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The induced-charge electrokinetic flow (ICEKF) in a rectangular micorchannel with conducting hurdles embedded in the middle is investigated in this paper. A correction method is suggested to numerically estimate the induced zeta potential on the conducting surface. Two-dimensional pressure-linked Navior-Stokes equation is used to model the flow field in the channel. The numerical results show flow circulations generated from the induced non-uniform zeta potential distribution along the conducting hurdle surfaces. It is demonstrated numerically that the local flow circulations provide effective means to enhance the flow mixing between different solutions; the degree of enhancement depends on the hurdle geometries and hurdle numbers. The mixing using ICEKF described in this paper can be used in various microfluidics and lab-on-a-chip applications.
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Wang, Yun, and Sung Chan Cho. "Multi-Dimensional Modeling of Lithium-Air Batteries." In ASME 2013 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/imece2013-66809.
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In this study, we develop a multi-dimensional model of lithium-air (Li-air) batteries to evaluate their performance. The model consists of a set of partial differential equations of species and charges conservation, in conjunction of the electrochemical reaction kinetics at the reaction interface, and takes into account two major mechanisms of voltage loss due to insoluble discharge products formation: namely, electrode passivation and increased oxygen transport resistance. The model is successfully implemented to numerical simulation of discharging operation of a two-dimensional Li-air battery. Highly non-uniform distributions of oxygen and insoluble products are revealed under high current density. The pore space in the electrode is not fully utilized, particularly under high discharging current operation. The fundamental model and numerical tool are important for developing high-performance Li-air batteries.
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Heuer, Tom, and Bertold Engels. "Numerical Analysis of the Heat Transfer in Radial Turbine Wheels of Turbo Chargers." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27835.
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Increasing exhaust gas temperatures of turbocharged Otto and Diesel engines make great demands on the durability of turbine wheels. Hence, a substantiated knowledge about the temperature distribution inside the turbine wheel is crucial. To obtain these temperatures the CHT-method has been applied to a radial turbine of a commercial Diesel turbocharger. The geometry and physical conditions are taken from gas stand tests. Hence, the model includes the entire wheel, the twin scroll housing, and the inlet and outlet pipe. In addition to aerodynamic boundary conditions, thermal boundary conditions have been obtained from gas stand tests. Thermocouples have been applied to blades, hub, back, and shaft close to the piston ring and near to the bearings. The signals have been transmitted via telemetry. A heat transfer investigation clarifies the essential heat transfer mechanisms. The interaction between fluid and solid leads to a non-uniform heat transfer direction, i.e. in some wheel regions heat is even discharged. A discussion about the influence of boundary conditions proves the need to implement not only the turbine wheel solid walls but to include each wall as a solid domain. Since CFD-results are strongly dependent on the boundary conditions, different models are discussed and their influence on the temperature distribution is shown.
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Lee, Samuel P., Simon M. Barrans, Martyn L. Jupp, and Ambrose K. Nickson. "Investigation Into the Impact of Span-Wise Flow Distribution on the Performance of a Mixed Flow Turbine." In ASME Turbo Expo 2018: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/gt2018-76992.
Full textAbstract:
Current trends in the automotive industry towards engine downsizing means turbocharging now plays a vital role in engine performance. A turbocharger increases charge air density using a turbine to extract waste energy from the exhaust gas to drive a compressor. Most turbocharger applications employ a radial inflow turbine. However, to ensure radial stacking of the blade fibers and avoid excessive blade stresses, the inlet blade angle must remain at zero degrees. Alternately, mixed flow turbines can offer non-zero blade angles while maintaining radial stacking of the blade fibers. The additional freedom to manipulate the blade leading edge and varying tip speed allow for varying leading edge incidence in the span-wise direction. Furthermore, the flow development in the volute does not necessarily lead to uniform inlet conditions. The current paper investigates the performance of a mixed flow rotor passage under a range of span-wise flow distributions including that produced by a turbine volute. Initial unsteady pulsating simulations were conducted and the volute exit flows extracted. These distributions were then applied as boundary conditions to a single passage model. All simulations were carried out at a constant MFP and average leading edge relative flow angle. It was observed that the different inlet flow distributions resulted in marked difference in passage flow characteristics. A 2.17% variation was observed between cases in the radial passage. A tilted passage was also included providing an increased axial flow component at the inlet. This passage was found to result in greater swallowing capacity when compared to that of the radial passage.
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Takakuwa, Osamu, Junichiro Yamabe, Hisao Matsunaga, Yoshiyuki Furuya, and Saburo Matsuoka. "Recent Progress on Interpretation of Tensile Ductility Loss for Various Austenitic Stainless Steels With External and Internal Hydrogen." In ASME 2017 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/pvp2017-65671.
Full textAbstract:
Slow-strain rate tensile (SSRT) tests on various metals having γ-Fe phase; Type 304 and 316L stainless steels, HP160 high strength stainless steel, and A286 Fe-based super alloy were conducted in external hydrogen and with internal hydrogen. The external hydrogen indicates non-charged specimens tested in high-pressure hydrogen-gas environment, whereas the internal hydrogen indicates hydrogen-charged specimens, with uniform distribution of hydrogen, tested in inert gas. The hydrogen distribution was calculated based on the measured hydrogen diffusivity and solubility. The fracture morphologies were observed by scanning electron microscopy (SEM). For Types 304, 316L, and HP160, the relative reduction in area (RRA) of the steels was successfully reproduced by the nickel equivalent, Nieq, showing the higher Nieq, the lager RRA. Furthermore, at a low Nieq, the RRA of the steel with external hydrogen was nearly equal to that with internal hydrogen. In contrast, at a high Nieq, the RRA of the steel with internal hydrogen was slightly degraded by hydrogen, RRA ≈ 0.8, whereas that in external hydrogen was not degraded, RRA ≈ 1. For A286, despite a high Nieq, the RRA of the alloy with internal hydrogen was significantly degraded by hydrogen, RRA ≈ 0.5. The fracture morphologies were categorized into four types: quasi-cleavage fracture associated with hydrogen-assisted surface cracks; ordinary void formation with no hydrogen effect; small-void formation associated with void sheet enhanced by hydrogen; facet formation induced by hydrogen. These categorized morphologies could be interpreted in terms of hydrogen distribution (internal or external hydrogen), austenitic stability (a low or high Nieq), and microstructure (solution or precipitation-hardened treatment).