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Статті в журналах з теми "Charge de Rayleigh"
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Post, Scott L., and Rory L. Roten. "A Review of the Effects of Droplet Size and Flow Rate on the Chargeability of Spray Droplets in Electrostatic Agricultural Sprays." Transactions of the ASABE 61, no. 4 (2018): 1243–48. http://dx.doi.org/10.13031/trans.12516.
Повний текст джерелаАнотація:
Abstract. The chargeability of liquid sprays is an important factor in determining the deposition efficiency of electrostatic pesticide sprays. The Rayleigh limit provides information on the maximum amount of charge a spray droplet can carry as a function of droplet size and liquid properties. This article reviews the literature to determine what fraction of the Rayleigh limit is achievable. Typically, less than 10% of the Rayleigh limit charge is obtained. The droplet charge per unit mass decreases with increasing droplet size and liquid flow rate. A correlation equation is derived from published data to predict spray droplet charge per unit mass from droplet size, flow rate, and charging voltage. Keywords: Droplet size, Electrostatic charging, Spray drift, Sprayers, Ultra-low volume spraying.
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Airey, M. W., R. G. Harrison, K. L. Aplin, C. Pfrang, and B. McGinness. "Electrical effects on droplet behaviour." Journal of Physics: Conference Series 2702, no. 1 (February 1, 2024): 012015. http://dx.doi.org/10.1088/1742-6596/2702/1/012015.
Повний текст джерелаАнотація:
Abstract The effect of charge on water droplets modulates various aspects of their behaviour. These include the droplet stability, evaporation, and lifetime. Microphysical models have been developed such that a reasonably good understanding of these processes has been achieved. However, the specific effects of charge deserve further scrutiny as they are an intrinsic component of the factors controlling droplet characteristics. Describing the effects of these requires an understanding of the electrostatic pressure present in the droplet and its surface tension. One way to test these effects and assess droplet response to charge is to take an experimental approach to make observations directly. In this study, individual droplets are levitated in an acoustic wave to allow isolated measurements to be taken. The droplets are monitored using a CCD camera with a microscope objective lens. In some cases, with sufficient charge present, effects on droplet stability can be observed as Rayleigh explosions, where a sudden drop in mass is seen superimposed on the evaporation profile. These events also allow the charge on the droplet to be calculated, which is then compared with the droplet evaporation. Another factor that plays a part in droplet behaviour is droplet composition. Different substances have different surface tension, and this is explored by performing some experiments on sulphuric acid droplets. Theory predicts that the more highly charged a droplet is, the more resistant to evaporation it becomes. Experimental data collected during this study agrees with this, with more highly charged droplets observed to have slower evaporation rates. However, highly charged drops were also observed to periodically become unstable during evaporation and undergo Rayleigh explosions. Each instability of a highly charged drop removes mass, reducing the overall droplet lifetime regardless of the slower evaporation rate. The sulphuric acid droplets were observed to be much more resistant to evaporation and no Rayleigh instabilities were observed.
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Novo, Carolina, and Paul Mulvaney. "Charge-Induced Rayleigh Instabilities In Small Gold Rods." Nano Letters 7, no. 2 (February 2007): 520–24. http://dx.doi.org/10.1021/nl062649t.
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Singh, Baljeet, Asha Sangwan, and Jagdish Singh. "Nonlocal effects on Rayleigh-type surface wave in a micropolar piezoelectric medium." Vietnam Journal of Mechanics 44, no. 1 (March 30, 2022): 1–13. http://dx.doi.org/10.15625/0866-7136/16539.
Повний текст джерелаАнотація:
The properties of Rayleigh-type surface wave in a linear, homogeneous and transversely isotropic nonlocal micropolar piezoelectric solid half-space are explored. Dispersion relations for Rayleigh-type surface wave are derived for both charge free and electrically shorted cases. Using an algorithm of iteration method in MATLAB software, the wave speed of Rayleigh wave is computed for relevant material constants. The effects of nonlocality, angular frequency, micropolarity and piezoelectricity are illustrated graphically on the propagation speed of Rayleigh wave.
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Basavaraju, G., Lynn Kissel, John C. Parker, R. H. Pratt, S. C. Roy, and S. K. Sen Gupta. "Rayleigh scattering by atomic ions of low nuclear charge." Physical Review A 34, no. 3 (September 1, 1986): 1905–11. http://dx.doi.org/10.1103/physreva.34.1905.
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Tung, Do Xuan. "Dispersion equation of Rayleigh waves in transversely isotropic nonlocal piezoelastic solids half-space." Vietnam Journal of Mechanics 41, no. 4 (December 28, 2019): 363–71. http://dx.doi.org/10.15625/0866-7136/14621.
Повний текст джерелаАнотація:
This study is devoted to investigate the propagation of Rayleigh-type waves in transversely isotropic nonlocal piezoelastic half-space. When the stress-free boundary is maintained at charge-free condition, the dispersion equation for the propagation of Rayleigh waves at the free surface of transversely isotropic piezoelastic solids has been obtained. Based on the obtained dispersion equation, the effect of the nonlocality on the speed of Rayleigh wave is numerically considered. The dependence of velocities of plane waves in transversely isotropic nonlocal piezoelastic medium on the direction of propagation as well as non-dimensional frequency parameter has been also illustrated.
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Wang, C. H., J. N. Woodford, C. Zhang, and L. R. Dalton. "Resonant and nonresonant hyper–Rayleigh scattering of charge-transfer chromophores." Journal of Applied Physics 89, no. 8 (April 15, 2001): 4209–17. http://dx.doi.org/10.1063/1.1354636.
Повний текст джерела
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Akrour, Dalila, Mohamed Issam Elkhazen, Walid Hassen, Karim Kriaa, Chemseddine Maatki, Bilel Hadrich, and Lioua Kolsi. "Numerical Investigation of the Electro-Thermo Convection in an Inclined Cavity Filled with a Dielectric Fluid." Processes 11, no. 8 (August 20, 2023): 2506. http://dx.doi.org/10.3390/pr11082506.
Повний текст джерелаАнотація:
The present work is a numerical analysis of electro-thermo convection, occurring in a square differentially heated cavity filled with a dielectric fluid. The cavity experiences the combined effects of viscous, electrical, and thermal forces. The equations modelling the physical problem are solved via the finite volume approach. The study focuses on the effect of cavity tilt on the fluid flow structure and thermal performance inside the enclosure under the action of an electric field. A parametric study was performed, where the tilt angle is getting varied between 0° and 90°, as well as the Rayleigh number (5000 ≤ Ra ≤ 250,000) and the electric field (0 ≤ T ≤ 800). Furthermore, the electric charge injection level C, the mobility M and the Prandtl Pr numbers were all adjusted to a value of 10. The obtained results demonstrate that the hydrodynamic and thermal fields are significantly impacted by the cavity inclination. In addition, regardless of the thermal Rayleigh’s number, high electric field values could govern fluid movement through electric forces. Electro-convection typically demonstrates an oscillating flow due to the tilting of the cavity which gives rise to a bicellular regime occupying the entire cavity. A correlation has been established to estimate heat transfer by considering various system parameters such as cavity inclination, electrical Rayleigh number, and thermal Rayleigh number.
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Langdon-Arms, Samuel, Michael Gschwendtner, and Martin Neumaier. "Rayleigh-Taylor instability in oscillating liquid pistons." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 233, no. 4 (April 27, 2018): 1236–45. http://dx.doi.org/10.1177/0954406218768836.
Повний текст джерелаАнотація:
In this study, an experimental apparatus is used to excite four U-tube-shaped liquid pistons connected in series, and to study their behaviour. Some of the gas spaces are heated to induce piston oscillations; in others, gas expansion is utilised to produce a refrigeration effect. It was discovered that the liquid piston surface would become unstable and turbulent at relatively low gas charge pressures (2 bar–3 bar). Cylindrical polyethylene floats were employed at each piston surface in order to reduce the area of the free surface of each piston and allow experiments to be conducted over a wide range of operating conditions. Experiments were carried out using gas charge pressures in the range of 1 bar–6 bar. The resulting liquid piston oscillations were measured and analysed to assess the impact of any developing piston instability. Evidence of a liquid piston acceleration limit, likely resulting from the Rayleigh-Taylor instability phenomenon, is consistently observed during the experiments. The use of submerged polyethylene piston floats is found to increase the surface stability and enable maximum accelerations of 25 ms−2 to 30 ms−2.
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Wang, Xiaoyi, Wenyu Hu, Yang Qiu, Yi Huang, Xueqing Wang, Min Xu, Jian Ma, et al. "Directional charge transportation and Rayleigh scattering for the optimal in-band quantum yield of a composite semiconductor nano-photocatalyst." Catalysis Science & Technology 11, no. 11 (2021): 3855–64. http://dx.doi.org/10.1039/d0cy02316g.
Повний текст джерелаАнотація:
The work propose a novel technique based on wavelength dispersive in situ photoluminescence spectroscopy for diagnosing the wavelength dependent directional charge transportation and Rayleigh scattering enhanced in-band quantum yield.
Дисертації з теми "Charge de Rayleigh"
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Cantegril, Thomas. "Étude de l’électrisation de gouttes de carburant aéronautique." Electronic Thesis or Diss., Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2024. http://www.theses.fr/2024ESMA0031.
Повний текст джерелаАнотація:
Le secteur aéronautique doit relever des défis environnementaux majeurs pour les décennies à venir. Afin de réduire son impact environnemental, des objectifs ambitieux ont été fixés par des instances comme l’ACARE, visant une neutralité carbone d'ici 2050. Parmi ces objectifs, une réduction de 90 % des émissions d’oxydes d’azote par rapport à 2000, une baisse de 55 % des émissions de CO₂ d’ici 2030 par rapport à 1990 comme une diminution des particules fines et des traînées de condensation sont donc attendus. Pour y parvenir, l’amélioration de la combustion dans les moteurs, principale source de ces émissions, est cruciale. Un des leviers d’optimisation est l’atomisation, qui contrôle la distribution du combustible dans la chambre de combustion. Une atomisation maîtrisée réduit les zones riches en carburant, limitant ainsi la formation de particules fines. Actuellement, des systèmes aéromécaniques génèrent de fines gouttelettes via des jets d’air et des orifices calibrés. Une alternative prometteuse est l’électro-atomisation, qui utilise des champs électriques intenses pour produire des gouttelettes de petites dimensions. Cette thèse explore l’électro-atomisation et son potentiel pour l’aéronautique. Les propriétés électriques de deux carburants – un kérosène et un mélange substitut composé de dodécane et d’éthanol – sont analysées à différentes températures, notamment leur conductivité et permittivité électriques. Ces caractéristiques permettent de comprendre la capacite de chargement électrique des liquides diélectriques. Un banc expérimental dédié a été développé pour étudier la production de gouttes à faibles débits sous haute tension. L’influence du débit et de la tension sur la taille et la charge électrique des gouttes est analysée, avec pour objectif d’approcher la charge de Rayleigh, seuil où une goutte explose pour former des gouttelettes plus fines, ce qui pourrait améliorer la combustion. Cette analyse étudie également l’équilibre entre forces électriques et tension superficielle dans la formation des gouttesThe aviation sector must address major environmental challenges in the coming decades. To reduce its environmental impact, ambitious targets have been set by organizations such as ACARE, aiming for carbon neutrality by 2050. These goals include a 90% reduction in nitrogen oxide emissions compared to 2000, a 55% decrease in CO₂ emissions by 2030 relative to 1990, as well as a reduction in fine particulate matter and contrail formation. Achieving these objectives requires improvements in combustion within engines, location of the main source of these emissions. One key optimization lever is atomization, which could controls the distribution of kerosene in the combustion chamber. Effective atomization minimizes fuel-rich zones, thereby reducing the formation of fine particles. Currently, aerodynamic systems generate fine droplets using air jets and calibrated orifices. A promising alternative is electro-atomization, which utilizes strong electric fields to produce droplets.This thesis explores electro-atomization and its potential for the aviation industry. The electrical properties of two fuels—a kerosene and a substitute mixture of dodecane and ethanol—are analyzed at different temperatures, focusing on their electrical conductivity and permittivity. These properties provide insights into the charging behavior of dielectric liquids.A dedicated experimental setup has been developped to study droplet production at low flow rates under high voltage. The influence of flow rate and voltage on droplet size and charge is analyzed, with the objective to approach the Rayleigh charge limit, a threshold at which a droplet explodes into finer droplets, potentially enhancing combustion. This analysis also examines the balance between electric forces and surface tension in droplet formation
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Santos, Leandra Pereira dos 1985. "Eletrização de líquidos e sólidos : excessos de carga e efeito sobre as propriedades de superfície." [s.n.], 2013. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250321.
Повний текст джерелаАнотація:
Orientador: Fernando GalembeckTese (doutorado) - Universidade Estadual de Campinas, Instituto de Química
Made available in DSpace on 2018-08-25T12:45:16Z (GMT). No. of bitstreams: 1 Santos_LeandraPereirados_D.pdf: 6636066 bytes, checksum: 1088753dac4139ce09351108770ac021 (MD5) Previous issue date: 2013
Resumo: Nesta tese, investigou-se a eletrização e os mecanismos de acúmulo de carga em gotas de água e filmes de polietileno, bem como, avaliou-se o efeito das cargas elétricas em algumas propriedades desses materiais. A eletrização de água foi realizada de duas formas: pelo contato com uma superfície metálica polarizada ou expondo as gotas de água a um potencial eletrostático criado através do ar por um eletrodo sem contato. Em ambos os casos, observou-se que a água adquire excesso de cargas e que o valor detectado excede o limite de Rayleigh em algumas dezenas. Verificou-se que a presença de cargas em gotas de água leva à diminuição de sua tensão superficial e ao aumento espontâneo de sua área, por outro lado, não foi observada mudança na sua densidade. O reconhecimento desses fatos deve contribuir para uma maior compreensão de vários fenômenos eletrostáticos que ocorrem na presença de água em estado líquido ou adsorvida. A superfície superior e inferior de filmes de polietileno expostos à descarga corona adquire potencias elevados e opostos formando um filme dipolar. No entanto, a molhabilidade, a composição química e a rugosidade das duas superfícies são bastante diferentes. Enquanto a superfície superior é modificada pelo tratamento corona, a superfície inferior, apesar de se tornar eletrizada, permanece inalterada após o tratamento. Estes resultados mostram que a eletrização da superfície voltada para o eletrodo corona ocorre por um processo diferente da superfície oposta. A eletrização da superfície inferior durante o processo corona abre possibilidades para aplicações onde seja desejável ter um filme eletrizado, porém sem modificar as características originais da superfície
Abstract: In this thesis, we investigated charging process and the mechanism of charge build-up in water droplets and polyethylene films as well. We evaluated the effect of electrical charges on some properties of these materials. Charging of water drops was done using two different methods by: contacting an electrified metal or exposing water to the electrostatic potential created through air by a noncontacting biased electrode. In both cases, water drops acquire net electric charge and its value exceeds the Rayleigh limit in a few tens. It was verified that the presence of charges in water droplets leads to reduced surface tension and increased spontaneous its area, but there was no change in density. Recognition of these facts should contribute to further understanding of various electrostatic phenomena taking place in the presence of liquid or adsorbed water. Top and bottom surfaces of polyethylene (PE) films exposed to corona discharge display large and opposite electrostatic potentials, forming an electric bilayer. However, water wetting, chemical composition and roughness of the two surfaces are quite different. While the top surface is modified by corona treatment, the bottom surface is charged but remains unchanged after treatment. These results show that poling the surface closer to the corona electrode triggers another but different charge build-up process at the opposite surface. Charging of the bottom surface during corona opens possibilities for applications where it is desirable to have a polymer film charged, but without modifying the original characteristics of the surface
Doutorado
Físico-Química
Doutora em Ciências
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Saidi, Mohamed. "Mesure et analyse de l'état de déformation et d'endommagement interne dans les composites à matrice cimentaire utilisés pour le renforcement des structures de génie civil." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSE1092.
Повний текст джерелаАнотація:
Les composites à matrice cimentaire et renforts textiles, du fait de leur compatibilité mécanique, environnementale et esthétique, sont utilisés sur une large échelle pour la réhabilitation et le renforcement du patrimoine bâti et des ouvrages du génie civil. Sous l'effet de sollicitations mécaniques ou environnementales, les phénomènes d'interaction et d'endommagement entre le renfort textile et la matrice cimentaire s'avèrent plus complexes que dans le cas des composites à matrice polymères. Celles-ci sont liées principalement au comportement fissurant du composite, à la nature fragile de la matrice et à l'adhérence renfort/matrice à prépondérance mécanique. Plus particulièrement, la connaissance et la compréhension des mécanismes de transfert de charge à l'interface renfort/matrice et l'initiation des fissures restent des verrous scientifiques majeurs.Les techniques de mesure classiques utilisées pour la caractérisation du comportement mécanique des composites à matrice cimentaire (extensomètres mécaniques, corrélation d'image digitale, etc.) sont en mesure de donner des informations sur l'état de déformation et de contrainte de la surface du corps d'épreuve. Les différents mécanismes de sollicitation et de dégradation des composants (renfort, matrice, interface) sont déduits en utilisant les approches de la mécanique des milieux continus et de la rupture.Dans ce contexte, ce travail a pour finalité la mise en place et l'adaptation d'un système de mesure intégrable à l'intérieur des composites : capteurs à base de fibres optiques distribuées. Cette technique de mesure est couplée à la corrélation d'image digitale et des jauges en surface des composites. L'objectif principal est d'analyser plus finement les paramètres mécaniques à l'échelle micro et les mécanismes de transfert de charge, d'initiation et de propagation de fissures, ainsi que les mécanismes d'endommagement. Sur la base d'essai de traction uni-axiale couplé à l'instrumentation choisie, une méthodologie d'identification de lois locales d'interaction renfort/matrice est mise en œuvre. La finalité du travail de thèse sera, grâce à ces lois locales, de déterminer les paramètres matériels du composite (longueur de transfert de charge, contrainte de cisaillement à l'interface renfort/matrice, etc.), et l'établissement des paramètres mécaniques caractéristiques du comportement local (fissuration, endommagement, comportement des interfaces, etc.) et global (lois de comportement, ouverture des fissures). Neuf configurations sont testées et analysées dans ce travail : deux types de matrice, deux types de renfort textile et trois taux de renfort. L'adaptation du protocole expérimental et la fiabilité des résultats obtenus sont validées. Le comportement global et local du composite, de la matrice, du textile et de l'interface sont mesurés et analysés. La longueur de transfert de charge, la contrainte de cisaillement à l'interface textile/matrice, l'endommagement de l'interface et l'ouverture des fissures sont quantifiés et discutés. Les effets du taux de renfort, du type de la matrice et du textile, des paramètres mécaniques et géométriques du composite sur sa réponse mécanique en traction sont identifiés et évalués. Ces résultats sont utilisés pour le perfectionnement et/ou le développement des modèles mécaniques du comportement en rigidité et à la rupture des composites à renfort textile et matrice cimentaireDue to their mechanical, environmental and aesthetic compatibility, textile reinforced cementitious matrix composites are used on a large scale for rehabilitation and reinforcement of the built heritage and civil engineering structures. Under the effect of mechanical or environmental loads, the phenomena of interaction and damage between the textile reinforcement and the cementitious matrix are more complex than in the case of polymer matrix composites. These are mainly related to the cracking behaviour of the composite, the fragile nature of the matrix and the behaviour of the reinforcement/matrix bond. In particular, knowledge and understanding of the load transfer mechanisms at the reinforcement/matrix interface and crack initiation remain a major scientific challenge.Conventional measurement techniques used to characterise the mechanical behaviour of cementitious matrix composites (mechanical extensometers, digital image correlation, etc.) are able to provide information on the strain and stress state at the surface of a tested specimen. The different mechanisms of internal forces and degradation of the components (reinforcement, matrix, interface) are deduced using approaches of continuum and fracture mechanics.In this context, this work aims at implementing and adapting a measurement system that can be integrated into the core of composites: distributed optical fibre sensors. In order to check its reliability, this measurement technique is coupled with classical extensometer technics such as strain gauges implemented on the surface of the composites and digital image correlation. The main objective is to analyse more precisely the mechanical parameters at the micro scale and the load transfer mechanisms, crack initiation and propagation as well as damage mechanisms. On the basis of uni-axial tensile tests, coupled with the chosen instrumentation, a methodology for identifying local laws of reinforcement/matrix interaction is implemented. The aim of the thesis work is, using these local laws, to determine the micro-mechanical parameters of the composite (load transfer length, shear stress at the reinforcement/matrix interface, etc.) and to establish parameters characteristic of the local and global behaviour (cracking pattern and crack opening, damage indicators, constitutive equations, etc.). Nine configurations are tested and analysed in this work: two types of matrix, two types of textile reinforcement and three reinforcement ratios. The adaptation of the experimental protocol and the reliability of the results obtained are validated. The global and local behaviour of the composite, matrix, textile and their interface are measured and analysed. Load transfer length, shear stress at the textile/matrix interface, interface damage and crack opening are quantified and discussed. The effects of reinforcement ratio, matrix and textile type, mechanical and geometrical parameters of the composite on its mechanical tensile response are identified and evaluated. These results are used for the refinement and/or development of mechanical models of the stiffness and fracture behaviour of textile and cement-matrix reinforced composites
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Baigl, Damien. "Etude expérimentale de polyélectrolytes hydrophobes modèles." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2003. http://tel.archives-ouvertes.fr/tel-00003620.
Повний текст джерелаАнотація:
Un polyélectrolyte hydrophobe est un polymère portant des charges électriques lorsqu'il est en solution aqueuse et dont l'eau est un mauvais solvant pour le squelette. Cette thèse a pour objectif d'établir l'influence de la nature hydrophobe du squelette sur les propriétés physiques des polyélectrolytes. Pour cela, nous avons tout d'abord synthétisé une série de poly(styrène-\emph(co)-styrènesulfonate de sodium), appelés PSS, possédant des taux de charge $f$ variant entre 30\% et 100\% et comportant entre $N=120$ et $N=2520$ monomères par chaîne. Ces PSS sont caractérisés précisément et peuvent être considérés comme des polyélectrolytes hydrophobes modèles. Nous avons alors étudié leurs propriétés volumiques puis interfaciales.\\ \emph(1. Propriétés en volume.) Le taux de charge effectif de la chaîne unique est anormalement réduit par rapport au cas du polyélectrolyte hydrophile. D'autre part, les propriétés structurales ont été caractérisées par la diffusion des rayons X et la technique de la sonde colloïdale en microscopie à force atomique (AFM). La conformation des chaînes se fait ressentir puisque la longueur de corrélation varie comme $N^0C_p^(-\alpha)$ où $C_p$ est la concentration en polymère et $\alpha$ un exposant dépendant de $f$, décroissant de 1/2 ($f=100\%$) à 1/3 au voisinage de la limite de solubilité. Ces observations sont interprétées dans le cadre d'un modèle théorique prédisant la conformation de la chaîne isolée comme un collier de perles, constitué de globules denses (les perles) reliés deux à deux par un segment de chaîne étirée. La dynamique collective des chaînes, quant à elle, est très proche de celle des polyélectrolytes hydrophiles.\\ \emph(2. Propriétés aux interfaces.) Nous avons conçu une expérience permettant, par adsorption électrostatique ou hydrophobe, de fixer les chaînes de PSS sur une surface solide plane modifiée chimiquement. La couche de PSS adsorbée, immergée dans l'eau, est caractérisée $in~situ$ par ellipsométrie, réflectivité des rayons X haute énergie et microscopie à force atomique. Nous avons ainsi trouvé que la taille de perles varie entre 1 et 5 nm en fonction de $f$. Cette variation est en parfait accord avec les prédictions du modèle dit du collier de perles. Enfin, les polyélectrolytes hydrophobes s'adsorbent également aux interfaces hydrophobes, les perles, dans certains cas, s'étalant sur la surface.
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Alghamdi, Amani Saeed. "Study of Generalized Lomax Distribution and Change Point Problem." Bowling Green State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1526387579759835.
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Bruneton, Marianne. "Etude de la structure lithosphérique 3D du bouclier balte par l'analyse des ondes de Rayleigh." Phd thesis, Université Joseph Fourier (Grenoble), 2003. http://tel.archives-ouvertes.fr/tel-00719966.
Повний текст джерелаАнотація:
La tomographie sismologique à l'échelle régionale peut donner des informations sur la structure profonde des continents anciens. Nous développons une méthode de tomographie en ondes de surface, puis nous l'appliquons aux ondes de Rayleigh du projet SVEKALAPKO (bouclier Balte). Cette méthode est basée sur le tracé de rais 2D, elle tient compte de la courbure des fronts d'onde incidents. Le profil moyen en vitesse des ondes S obtenu est de 4% plus rapide que des modèles de Terre standards et ne présente pas de zone à moindre vitesse. La comparaison avec des données issues de xénolithes implique une stratification chimique de la lithosphère. Le modèle 3D présente des variations latérales de +/-3% attribuées à des différences de composition des roches. La limite Archéen-Protérozoïque n'a pas de signature nette peut-être à cause d'une modification du manteau à grande échelle au cours du Protérozoïque et/ou de la structure complexe du domaine Protérozoïque, héritée de sa formation.
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Noël, Justine. "Étude de la convection naturelle dans les matériaux à changement de phase." Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0062.
Повний текст джерелаАнотація:
Les matériaux à changement de phase (MCP) sont très utilisés pour le stockage de l'énergie thermique. Cependant, le temps de stockage/déstockage peut être important. La convection naturelle au sein du MCP permet de réduire ce temps et d'améliorer la fusion. Cette thèse propose l'étude expérimentale des effets de convection dans les MCP. Ces matériaux sont généralement opaques et les mesures optiques sont par conséquent difficiles à mettre en œuvre. Pour contrer ce problème, l'étude est réalisée par mesure IRM (Imagerie par Résonance Magnétique). L'IRM permet d'obtenir des cartographies de phases, température et vitesses et ainsi comprendre localement les mécanismes thermiques et hydrodynamiques mis en jeu. Deux matériaux types sont étudiés : un alcane avec un unique point de fusion, l'hexadécane, et un polymère présentant une plage de température de fusion, le polyéthylène glycol. La dispersion des longueurs de chaînes de ce polymère induit lors de la transition solide-liquide la présence d'une zone molle. La première partie de ce travail se concentre sur la caractérisation de ces MCP afin de connaître leurs propriétés en phase liquide, en phase solide et lors du changement de phase. De nombreuses méthodologies ont été développées et utilisées afin d'obtenir les propriétés thermiques (conductivité thermique, capacité calorifique, chaleur latente et masse volumique). Le comportement sous écoulement est étudié par rhéométrie en phase liquide et en changement de phase. Ces matériaux présentent une hystérésis entre la température de fusion et la température de solidification. Cette dernière est très dépendante des conditions thermiques et cinétiques appliquées pendant le changement de phase. Dans une seconde partie, l'effet de la convection est étudié. Il est montré que la convection démarre à partir d'un nombre de Rayleigh critique proche de 1430 pour l'hexadécane, validant les résultats théoriques de la littérature. La convection permet d'améliorer la hauteur de liquide d'un facteur quatre par rapport au régime conductif et d'augmenter la vitesse du front de fusion. Les transferts thermiques à la paroi sont nettement augmentés en convection. L'écoulement thermo-convectif affecte l'interface de fusion. Grâce aux cartographies de vitesses, nous avons pu observer que les régions de flux ascendants augmentent localement la hauteur liquide et que réciproquement les régions de flux descendants diminuent la hauteur liquide. Par opposition, en régime conductif, le front de fusion est plan et parallèle à la paroi chauffée. En présence de zone molle, l'interface solide-zone molle reste parallèle à la paroi et aucune vitesse supérieure à notre limite de détection (5*10^-5m/s) n'est observée dans la zone molle. La hauteur de la zone molle et de la phase solide sont réduites proportionnellement à leurs conductivités thermiques. Le développement de la convection dans la phase liquide est accompagné de l'apparition de motifs de convection correspondant à des hexagones (imparfaits). Lorsque la hauteur moyenne de liquide augmente, la longueur d'onde augmente également, de sorte que la longueur d'onde divisée par la hauteur liquide reste constante. Ces résultats sont similaires à ceux obtenus à la bifurcation primaire dans la convection classique de Rayleigh-BénardPhase change materials (PCMs) are widely used for thermal energy storage. However, the energy storage/release time can be important. Natural convection within the liquid PCM can reduce this time and improve melting. This thesis proposes the experimental study of the effects of convection on PCMs. As PCM are generally opaque, optical measurements are difficult to make. To address this issue, experiments are carried out using MRI (Magnetic Resonance Imaging) measurements. MRI allows to obtain phase, temperature and velocity maps and thus to understand locally the thermal and hydrodynamic mechanisms involved.Two PCMs are studied: a alkane with a single melting point, the hexadecane, and a polymer with a range of melting temperatures, the polyethylene glycol. The dispersion of the chain lengths of this polymer induces the presence of a mushy zone during the solid-liquid transition.The first part of the thesis focuses on the characterization of these PCMs in order to obtain their properties in liquid phase, in solid phase and during phase change. Many methodologies have been developed and used to obtain thermal properties (i.e. thermal conductivity, heat capacity, latent heat and density). The flow behavior is studied by rheometry for the liquid phase and during the phase change. These PCMs show a hysteresis between the melting and solidification temperatures. The latter is highly dependent on the thermal and kinetic conditions applied during the phase change.In a second part, the effect of convection is investigated. It is shown that convection starts from a critical Rayleigh number close to 1430 for hexadecane, in agreement with the theoretical results in the literature. Convection improves the liquid height by a factor of four compared to the conductive regime and increases the velocity of the melt front. Heat transfer at the wall is significantly increased when convection in present. The thermo-convective flow affects the melt interface. From velocity maps, we observed that the upward flow increases locally the liquid height, while the downward flow decreases it. In the conductive regime, the melt front is flat and parallel to the heated wall. In the presence of a mushy zone, its interface with the solid phase remains parallel to the top wall and no velocity higher than our detection limit (5*10^-5m/s) is observed within it. The heights of the mushy zone and solid phase decrease in proportion to their thermal conductivities. The development of convection in the liquid phase is coupled with the formation of convection patterns corresponding to (imperfect) hexagons. As the average liquid height increases, the wavelength of patterns also increases. This results in the wavelength divided by the liquid height remaining constant. These results are similar to those obtained at the primary bifurcation for the classical Rayleigh-Bénard convection
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Uguz, Kamuran Erdem. "Evaporative instability in binary mixtures." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112169/document.
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Cette étude concerne la physique des écoulements convectifs résultant d’une instabilité d’évaporation de fluides binaires. Ce problème a de nombreuses applications, l’enrobage par centrifugation, le dépôt de films, les caloducs, etc, pour lesquels le changement de phase et la convection jouent un rôle prépondérant dans la conception et la qualité des procédés. Le système physique étudié est un mélange liquide sous sa propre vapeur, confiné par deux plaques conductrices de chaleur et des bords latéraux isolants. Les plaques sont utilisées pour appliquer un gradient thermique. Aucun gradient de concentration n’est imposé au système. Ces gradients sont induits par les différentes vitesses d’évaporation des composés. Dans ce système, il est important de comprendre comment la dynamique des fluides et les transferts de masse et de chaleur entrent en compétition pour la formation de structures. Le principal objectif de ce travail est d’identifier les conditions pour que le système évolue d’un état conductif vers un état de convection lorsque le gradient vertical de température dépasse une certaine valeur critique.Dans le système, la convection s’installe par trois mécanismes distincts : évaporation, gradients de densité et gradients de tension interfaciale. Trois forces convectives s’opposent aux effets de diffusion qui tendent à garder le système en état conductif. Le seuil d’apparition de la convection dépend de quelques variables, comme les dimensions du contenant, les propriétés thermophysiques des phases liquide et vapeur, la fraction massique, et les caractéristiques de perturbations. L’effet de chacune de ces variables sur le seuil est étudié en présence ou non de gravité.Pour représenter la physique, un modèle mathématique non linéaire complet est développé, basé sur les conservations de quantité de mouvement, d’énergie et de masse dans chaque phase avec les conditions aux limites appropriées. Le fluide binaire est composé de deux alcools légers comme l’éthanol et le sec-butanol. Dans les équations du modèle, la masse volumique ainsi que la tension interfaciale sont fonctions à le fois de la température et de la concentration. Pour la recherche du seuil de transition, les équations sont linéarisées autour d’un état de base connu. Dans notre cas, il s’agit de l’état conductif. Le système d’équations linéaires résultant est résolu par une méthode de collocation spectrale Chebyshev.Nous obtenons quatre résultats principaux. Premièrement, dans un système multi-composants sans gravitation, une instabilité n’apparaît que lorsque le système est chauffé du côté de la phase vapeur contrairement à un système mono-composant. Cela implique que, si on souhaite éviter les instabilités, il vaut mieux un apport de chaleur par la phase liquide en cas de processus d’évaporation en couches minces ou en micro-gravité.Deuxièmement, en présence de gravité, un système multi-composants peut devenir instable quelle que soit la direction du chauffage. Si la convection thermique est négligeable, alors nous montrons que le chauffage par la phase vapeur est la configuration la plus instable. Sinon, les deux modes de chauffage sont à même de produire une instabilité. Ce résultat implique que le gradient thermique appliqué doit être inférieur à une valeur seuil pour éviter les instabilités quelle que soit la direction du chauffage.Troisièmement, lorsque l’instabilité apparaît en absence de gravité, des structures n’apparaitront pas dans le cas de fluide pur mais apparaitront dans le cas d’un fluide multi-composants. De même, des structures apparaitront en présence de gravité en fonction du facteur d’aspect du confinement. Les facteurs d’aspect peuvent être choisis pour éviter des structures multi-cellulaires même en cas d’apparition d’instabilités durant l’évaporation.Enfin, des structures oscillantes ne sont pas prédites de façon générale malgré les effets opposés des convections solutale et thermique dans le problème d’évaporationThis study focuses on understanding the physics of the convective flow resulting from evaporative instability in binary mixtures. This problem has wide applications in spin coating, film deposition, heat pipes, etc. where phase change and convection play a very important role in the design process and also final quality of the product. The physical system of interest consists of a liquid mixture underlying its own vapor sandwiched between two conducting plates with insulated sidewalls in a closed container. The conducting plates are used to apply a vertical temperature gradient while there is no applied concentration gradient in the system. Concentration gradients are induced by the different evaporation rate of the components. In this system it is important to understand how the fluid dynamics and the heat and mass transfer interact competitively to form patterns. The main goal of this work is to identify the conditions for the system going from the conductive no-flow state to a convection state when the applied vertical temperature gradient exceeds a certain value called the critical value.In the system convection arises due to three distinct phenomena; evaporation, density gradients, and interfacial tension gradients. These convective forces are opposed by the diffusion effects that try to keep the system in the conductive no-flow state. The onset point depends upon several variables such as the dimensions of the container, thermo-physical properties of both liquid and vapor phases, mass fraction, and the characteristic of the disturbance given to the system. The effects of each of these variables on the onset point are investigated both in the presence and in the absence of gravity. To represent the physics a complete non-linear mathematical model is developed including momentum, energy, and mass balances in both phases with appropriate boundary conditions. The binary mixture is assumed to be made up of two low weight alcohols such as ethanol and sec-butanol. In the modeling equations the density and the interfacial tension are taken to be function of both temperature and concentration. To identify the onset point the non-linear equations are linearized around a known base state. In this case the base state is the conductive no-flow state. The resulting set of linear equations is solved using a spectral Chebyshev collocation method. Four major results arise from this work. First, in a multi-component system in the absence of gravity, an instability arises only when the system is heated from the vapor side as opposed to evaporation in a single-component. The implication is that evaporative processes in thin layers or in micro-gravity are best conducted with heat from the liquid side if instabilities are to be avoided.Second, in the presence of gravity, a multi-component system may become unstable no matter the direction of heating. If thermal buoyancy is negligible then it is shown in this study that heating from the vapor side is the unstable arrangement. Otherwise either heating style can produce an instability. This result means that the applied temperature difference must be kept below a threshold in order to avoid flow instabilities no matter the heating direction.Third, whenever instability occurs in the absence of gravity, patterns will not result in the case of a pure component but may result in the case of multi-components. Likewise, patterns will result when gravity is taken into account provided the aspect ratio of the container lies in a suitable range. As a result, aspect ratios can be chosen to avoid multi-cellular patterns even if convective flow instabilities arise during evaporation.Lastly, oscillations are not ordinarily predicted despite opposing effects of solutaland thermal convection in the evaporation problem
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Vaněk, Stanislav. "Měření seismické činnosti pomocí optických vláknových senzorů." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2018. http://www.nusl.cz/ntk/nusl-376912.
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The aim of master's thesis is to get familiarized with the problems of measurement and analysis of seismic waves. Theoretical part deals with the description of seismic waves, especially their types, sources and properties. Attention was afterwards focused on the measurement systems of these waves, emphasis was placed on their principles and advantages. The practical part discusses methods of noise reduction and highlighting of significant events in measured data. At the end, individual methods are implemented into user-friendly graphical interface.
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Díez, Mikel. "Studies of the Mechanics and Structure of Shallow Magmatic Plumbing Systems." Scholar Commons, 2008. https://scholarcommons.usf.edu/etd/214.
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Volcanic activity, and the resultant deposits and structures at the Earth's surface, are the outcome of the inner workings of underground magmatic plumbing systems. These systems, essentially, consist of magma reservoirs which supply magma to the surface through volcanic conduits feeding volcanic eruptions. The mechanics and structure of plumbing systems remain largely unknown due to the obvious challenges involved in inferring volcanic processes occurring underground from observations at the surface. Nevertheless, volcanologists are beginning to gain a deeper understanding of the workings and architecture of magmatic plumbing systems from geophysical observations on active volcanoes, as well as from geological studies of the erosional remnants of ancient volcanic systems.
In this work, I explore the relationship between the structure and mechanics of shallow plumbing systems and the volcanic eruptions these systems produce. I attempt to contribute to the understanding of this complex relationship by linking geological and geophysical observations of an eroded basaltic subvolcanic system, and the eruptive and tectonic activity of an active volcano, with mathematical models of magma ascent and stress transfer.
The remarkable exposures of the Carmel outcrop intrusions, near the San Rafael swell, southeast Utah, U. S. A., allow detailed geological and geophysical observations of the roots of volcanic conduits that emerge from a subhorizontal magma feeder reservoir. These observations reveal a new mechanism for magma ascent and eruption triggering through gravitational instabilities created from an underlying feeding sill, and shed light on the mechanics of sill emplacement. Geophysical and geological observations of the 1999 and xii 1992 eruptions of the Cerro Negro volcano, Nicaragua, are used to explore the coupling between changes in the stress field and the triggering of volcanic eruptions, and magma ascent through the shallow crust. Modeling results of stress transfer and conduit flow highlight the importance of the surrounding stress field and geometry of the volcanic conduits that comprise shallow plumbing systems.
Книги з теми "Charge de Rayleigh"
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C, Herring G., Barros Toya, and Langley Research Center, eds. Demonstration of imaging flow diagnostics using Rayleigh scattering in Langley 0.3-Meter Transonic Cryogenic Tunnel. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1999.
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2
C, Herring G., Barros Toya, and Langley Research Center, eds. Demonstration of imaging flow diagnostics using Rayleigh scattering in Langley 0.3-Meter Transonic Cryogenic Tunnel. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1999.
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3
C, Herring G., Barros Toya, and Langley Research Center, eds. Demonstration of imaging flow diagnostics using Rayleigh scattering in Langley 0.3-Meter Transonic Cryogenic Tunnel. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1999.
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Lukaszuk, Katarzyna. Elektrooptische Absorptionsmessungen und Hyper-Rayleigh-Streuexperimente zur Bestimmung der Polarisierbarkeit zweiter Ordnung von Charge-Transfer-Komplexen. 1999.
Знайти повний текст джерелаЧастини книг з теми "Charge de Rayleigh"
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Hemdal, Stina, and Andrei N. Lipatnikov. "Investigation of Charge Mixing and Stratified Fuel Distribution in a DISI Engine Using Rayleigh Scattering and Numerical Simulations." In Advances in Engine and Powertrain Research and Technology, 187–206. Cham: Springer International Publishing, 2022. http://dx.doi.org/10.1007/978-3-030-91869-9_8.
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Samal, M. K. "Development of a Material Constitutive Model and Simulation Technique to Predict Nonlinearities in Piezoelectric Materials under Weak Electric Fields." In Mathematical Concepts and Applications in Mechanical Engineering and Mechatronics, 271–303. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-1639-2.ch013.
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Piezoceramic materials exhibit different types of nonlinearities depending upon the magnitude of the mechanical and electric field strength in the continuum. Some of the nonlinearities observed under weak electric fields are: presence of superharmonics in the response spectra and jump phenomena etc. especially if the system is excited near resonance. It has also been observed by many researchers that, at weak alternating stress fields, the relationship between the piezoelectrically induced charge and applied stress in ferroelectric ceramics, has the same form as the Rayleigh law (for magnetization versus magnetic field) in ferromagnetic materials. Applicability of the Rayleigh law to the piezoelectric effect has been demonstrated for Lead Zirconate Titanate ceramics by many researchers and their experimental results indicate that the dominant mechanism responsible for piezoelectric hysteresis and the dependence of the piezoelectric coefficient on the applied alternating stress is the pinning of non-180° domain walls. In this chapter, the Rayleigh law for ferromagnetic hysteresis has been modified and incorporated in a nonlinear electric enthalpy function and then applied in the analysis of hysteresis behavior of piezoelectric continua. Analytical solutions have been derived for a cantilever beam actuated by two piezo-patches attached to the top and bottom of the beam and excited by opposite electric fields. Analysis has been carried out at different electric field excitations of varying amplitude and frequencies and the results have been compared with the available experimental results from literature.
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He, Guang S. "Stimulated Rayleigh–Bragg Scattering." In Laser Stimulated Scattering and Multiphoton Excitation, 215–50. Oxford University Press, 2022. http://dx.doi.org/10.1093/oso/9780192895615.003.0007.
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In a two- or three-photon active liquid or solution, the input pump beam may interfere with the initial backward Rayleigh scattering beam to form a standing-wave field with a spatially periodic intensity modulation, which leads to the formation of an induced stationary Bragg grating through the intensity-dependent and multiphoton-resonance-enhanced refractive-index change of the scattering medium. The nonlinear reflection from the induced stationary Bragg grating provides the necessary gain to the backward Rayleigh scattering beam and may lead to a stimulated Rayleigh–Bragg scattering generation without any frequency shift. It has been shown that the primary contribution to the induced refractive index change is from the spatial redistribution of the multiphoton active solute molecules driven by the gradient force imposed by the standing-wave field.
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ZANETTI, Massimo, Francesca BOVOLO, and Lorenzo BRUZZONE. "Statistiques par différences pour les changements multispectraux." In Détection de changements et analyse des séries temporelles d’images 1, 247–303. ISTE Group, 2022. http://dx.doi.org/10.51926/iste.9056.ch9.
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Dans ce chapitre, nous introduisons deux modèles statistiques pour la description de la distribution des vecteurs de différences spectrales, et nous en tirons des méthodes de détection de changements basées sur une différence d'images. Le chapitre introduit d'abord le modèle standard à deux classes inchangé/changé pour la classification binaire. Lorsqu'on considère les informations de module, le modèle à deux classes peut être décrit par un mélange de distributions Rayleigh-Rice. L'estimation de paramètres de ce mélange est une tâche non triviale car ce modèle est non conventionnel. Par conséquent, une version de l'algorithme espérance-maximisation (EM), qui est adaptée spécifiquement au mélange Rayleigh-Rice, est présentée. Le chapitre propose alors une généralisation du modèle à deux classes inchangé/changé au cas multiclasse.
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Kumar, Samir, Prabhat Kumar, Anamika Das, and Chandra Shakher Pathak. "Surface-Enhanced Raman Scattering: Introduction and Applications." In Recent Advances in Nanophotonics - Fundamentals and Applications. IntechOpen, 2020. http://dx.doi.org/10.5772/intechopen.92614.
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Scattering of light by molecules can be elastic, Rayleigh scattering, or inelastic, Raman scattering. In the elastic scattering, the photon’s energy and the state of the molecule after the scattering events are unchanged. Hence, Rayleigh scattered light does not contain much information on the structure of molecular states. In inelastic scattering, the frequency of monochromatic light changes upon interaction with the vibrational states, or modes, of a molecule. With the advancement in the laser sources, better and compact spectrometers, detectors, and optics Raman spectroscopy have developed as a highly sensitive technique to probe structural details of a complex molecular structure. However, the low scattering cross section (10−31) of Raman scattering has limited the applications of the conventional Raman spectroscopy. With the discovery of surface-enhanced Raman scattering (SERS) in 1973 by Martin Fleischmann, the interest of the research community in Raman spectroscopy as an analytical method has been revived. This chapter aims to familiarize the readers with the basics of Raman scattering phenomenon and SERS. This chapter will also discuss the latest developments in the SERS and its applications in various fields.
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Maggiore, Michele. "Scattering of electromagnetic radiation." In A Modern Introduction to Classical Electrodynamics, 401–10. Oxford University PressOxford, 2023. http://dx.doi.org/10.1093/oso/9780192867421.003.0016.
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Abstract In this chapter we discuss the scattering of electromagnetic waves by charged particles. We define the scattering cross-section. We then consider the scattering of electromagnetic waves from free electrons, giving rise to the Thomson cross section, expressed in terms of the classical electron radius. We discuss the limit of validity imposed by quantum mechanics, and the corresponding Compton scattering. We then consider the scattering from electrons bound in atoms or molecules and compute the corresponding cross-section and resonant scattering. We conclude with the classic explanation, from Lord Rayleigh, of why the sky is blue, and why the Sun at sunset looks redder than at noon.
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Brown, John M. "Raman spectroscopy." In Molecular Spectroscopy. Oxford University Press, 1998. http://dx.doi.org/10.1093/hesc/9780198557852.003.0006.
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This chapter discusses Raman spectroscopy, which is based on a light scattering effect and named after the Indian physicist C.V. Raman, who was the first to observe it after A. Smekal had theoretically predicted it in 1928. Raman spectroscopy provides a way for obtaining information on the rotational and vibrational levels of a homonuclear diatomic molecule, which is not possible using rotational and rotational–vibrational spectra. The chapter also mentions Rayleigh scattering wherein the great majority of photons are scattered in all directions without a change in energy. The chapter illustrates how a modern Raman spectrometer probes light from a monochromatic source directed at the molecular sample. The scattered light is then viewed at right angles to the incoming beam. Its component wavelength is resolved with either a monochromator or an interferometer.
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Rojac, Tadej. "Piezoelectric Nonlinearity and Hysteresis Arising from Dynamics of Electrically Conducting Domain Walls." In Hysteresis in Engineering [Working Title]. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.98721.
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Macroscopic nonlinearity and hysteresis observed in the piezoelectric and dielectric responses of ferroelectric materials to external stimuli are commonly attributed to localized displacements of domain walls (DWs). The link between the macroscopic response and microscopic DW dynamics is provided by the well-known Rayleigh relations, extensively used to quantify the electrical and electromechanical behavior of ferroelectric ceramics and thin films under subswitching conditions. In this chapter, I will present an intriguing case where DWs exhibit enhanced electrical conductivity with respect to the bulk conductivity. By combining experimental data and modeling, it will be shown that the local conductivity, related to accumulation of charged points defect at DWs, does not only affect DW dynamics through DW-defect pinning interactions, as we may expect, but goes beyond it by affecting the macroscopic nonlinearity and hysteresis in a more complex manner. The major characteristics and implications of the underlying nonlinear Maxwell-Wagner piezoelectric relaxation, triggered by the presence and dynamics of conducting DWs, will be presented, reviewed and discussed in the framework of systematic multiscale analyses on BiFeO3 ceramics. The result may have implications in the development of promising BiFeO3-based compositions for high-temperature piezoelectric applications.
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Omer, Ala Eldin. "Review of Spectrum Sensing Techniques in Cognitive Radio Networks." In Advances in Wireless Technologies and Telecommunication, 85–107. IGI Global, 2019. http://dx.doi.org/10.4018/978-1-5225-5354-0.ch005.
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Most frequency spectrum bands are licensed to certain services to avoid the interference between various networks, but the spectrum occupancy measurements show that few portions of this spectrum are fully efficiently used. Cognitive radio is a future radio technology that is aware of its environment, internal state, and can change its operating behavior (transmitter parameters) accordingly. Through this technology the unlicensed users can use the underutilized spectrum without causing any harmful interference to the licensed users. Its key domains are sensing, cognition, and adaptation. The spectrum sensing problem is one of the most challenging issues in cognitive radio systems to detect the available frequency bands. This chapter introduces the concepts of various transmitter detection techniques, namely energy detection, matched filter detection, and cyclostationary feature detection. The chapter also discusses other sensing techniques that are introduced to enhance the detection performance of the conventional energy detector. Additionally, the introduced sensing techniques are implemented using extensive MATLAB simulations and their performances are evaluated and compared in terms of sensing time, detection sensitivity, and ease of implementation. The implementation is based on BPSK and QPSK modulation schemes under various SNR values for AWGN noisy channel with Rayleigh fading.
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Merveil Anague Tabejieu, Lionel, Blaise Roméo Nana Nbendjo, and Giovanni Filatrella. "Vibrations of an Elastic Beam Subjected by Two Kinds of Moving Loads and Positioned on a Foundation having Fractional Order Viscoelastic Physical Properties." In Advances in Dynamical Systems Theory, Models, Algorithms and Applications. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.96878.
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The present chapter investigates both the effects of moving loads and of stochastic wind on the steady-state vibration of a first mode Rayleigh elastic beam. The beam is assumed to lay on foundations (bearings) that are characterized by fractional-order viscoelastic material. The viscoelastic property of the foundation is modeled using the constitutive equation of Kelvin-Voigt type, which contain fractional derivatives of real order. Based to the stochastic averaging method, an analytical explanation on the effects of the viscoelastic physical properties and number of the bearings, additive and parametric wind turbulence on the beam oscillations is provided. In particular, it is found that as the number of bearings increase, the resonant amplitude of the beam decreases and shifts towards larger frequency values. The results also indicate that as the order of the fractional derivative increases, the amplitude response decreases. We are also demonstrated that a moderate increase of the additive and parametric wind turbulence contributes to decrease the chance for the beam to reach the resonance. The remarkable agreement between the analytical and numerical results is also presented in this chapter.
Тези доповідей конференцій з теми "Charge de Rayleigh"
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Perrot, J., J. Hainsworth, E. Marin, A. Morana, Y. Ouerdane, A. Boukenter, H. Boiron, J. Bertrand, and S. Girard. "Radiation Induced Refractive Index Change in Optical Fibres through Rayleigh-OFDR and FBG Techniques." In Bragg Gratings, Photosensitivity, and Poling in Glass Waveguides, BTu3A.3. Washington, D.C.: Optica Publishing Group, 2024. http://dx.doi.org/10.1364/bgpp.2024.btu3a.3.
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This study compares radiation-induced refractive index variations in SMF-28e+ fibres using Type II femtosecond-inscribed FBGs and R-OFDR techniques. It aims to understand femtosecond laser pulse effects on fibre core composition and behaviour in harsh environment.
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Friedman, Jonathan S., Mark W. Robison, Craig A. Tepley, Paul Castleberg, and Francisco Garcia. "Charge-Coupled-Device Detection for a Doppler-Rayleigh Lidar." In Optical Remote Sensing of the Atmosphere. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/orsa.1993.fa.4.
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The use of a charge-coupled device (CCD) camera together with a Fabry-Perot etalon (FP) to measure neutral winds in the thermosphere using 630 nm airglow has been proposed by Hays [1990]. In principle, the same technique is used for lidar winds with the sole difference being that a lidar provides its own light source, whereas airglow relies on a naturally occurring emission in the atmosphere. Hays [1990] showed that a CCD array detector attached to an etalon has more than an order of magnitude higher sensitivity than a photomultiplier tube (PMT). Particular advantages of using a CCD are: (1) It can record the whole fringe pattern at once, thus retaining the photons from multiple rings. (2) Because the FP etalon is not scanned, drifting of the location of the fringe pattern is eliminated. (3) The CCD has higher sensitivity to red light than a PMT. This paper is a report on the usefulness of a CCD array to record the fringes from a Doppler-Rayleigh lidar Fabry-Perot etalon for measuring winds and to compare the obtained results with those obtained using a scanning etalon and a PMT.
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Van de Walle, J., R. J. Tarento, and P. Joyes. "Localized charge Van der Waals ionic states above the Rayleigh limit." In Similarities and differences between atomic nuclei and clusters. AIP, 1997. http://dx.doi.org/10.1063/1.54569.
Повний текст джерела
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Hendrickx, E., T. Verbiest, K. Clays, and A. Persoons. "Molecular first hyperpolarisabilities of Bacteriorhodopsin and Retinal chromophores as determined from Hyper Rayleigh Scattering." In Organic Thin Films for Photonic Applications. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/otfa.1993.wc.4.
Повний текст джерелаАнотація:
In previous papers [1.2,3] we demonstrated the feasibility of the Hyper Rayleigh Scattering (HRS) technique for the determination of the first molecular hyperpolarizability β in a macroscopically isotropic solution. This technique has several advantages over the more classic electric field induced second harmonic generation (EFISHG) technique because no electric field is required to break the centrosymmetry of the solution. Consequently, HRS allows for an easy and accurate determination of β of charged molecules and of molecules where β originates from octopolar charge distributions. Here we demonstrate the full strength of the HRS technique by measuring the first hyperpolarisability of a protein in a buffer solution as well as the (charged) protein chromophores in different solvents.
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Verbiest, T., E. Hendrickx, A. Persoons, and K. Clays. "Measurements of molecular optical Hyperpolarisabilities using Hyper-Rayleigh Scattering." In Nonlinear Optics. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/nlo.1992.fb4.
Повний текст джерелаАнотація:
In this paper we report on new experiments of Hyper-Rayleigh Scattering (HRS) in solution, i.e. incoherent second harmonic light scattered from solutions illuminated by intense (IR) laser pulses. The HRS-technique, developed recently1, allows an accurate and easy determination of first order hyperpolarisabilities β of molecules. The great advantage of HRS as compared to electric field induced second harmonic generation (EFISHG, the other technique to determine β) is the absence of an orienting electric field to reduce the intrinsic symmetry of an isotropic solution. As a consequence data on the dipole moments are not needed and local field correction factors are unnecessary. HRS allows the determination of β of ionic species and will be the method of choice for the investigation of apolar molecules where p originates from octopolar charge distributions.2
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Avramov-Zamurovic, Svetlana, K. P. Judd, S. Matt, R. A. Handler, and A. T. Watnik. "The impact of optical turbulence created by Rayleigh Benard convection on vortex structure in beams carrying orbital angular momentum." In Propagation Through and Characterization of Atmospheric and Oceanic Phenomena. Washington, D.C.: Optica Publishing Group, 2022. http://dx.doi.org/10.1364/pcaop.2022.pw1f.1.
Повний текст джерелаАнотація:
We simulate Rayleigh Benard natural convection in air and propagate Gaussian Laguerre beams with varying topological charge through it. We present the impact of the optical turbulence on the phase and intensity of the beams.
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Guildenbecher, Daniel R., and Paul E. Sojka. "Secondary Breakup of Electrically Charged Newtonian Drops." In ASME 2007 International Mechanical Engineering Congress and Exposition. ASMEDC, 2007. http://dx.doi.org/10.1115/imece2007-41898.
Повний текст джерелаАнотація:
An experimental investigation was conducted to determine the secondary breakup morphology of electrically charged drops. Movies of drop breakup in a high speed air stream were recorded for drops charged between 0 and 60% of the Rayleigh charge limit. The conventional Weber number was found to be insufficient to classify the breakup morphology of charged drops. Rather an electrostatic Weber number was defined to account for the presence of the electrostatic surface stress. When the electrostatic Weber number was used in place of the classical Weber number, the observed breakup morphology was found to be similar to that proposed by previous researchers for uncharged drops. It is therefore concluded that secondary breakup of electrically charged drops can be characterized using the wealth of available literature on uncharged Newtonian drops, provided the electrostatic Weber number is used, and that the charge relaxation time is much smaller than the breakup time.
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Yang, Qingzhen, Zhengtuo Zhao, Ben Q. Li, and Yucheng Ding. "A Phase Field Modeling Study of the Rayleigh-Taylor Instability Subject to a Horizontal Electric Field." In ASME 2013 Heat Transfer Summer Conference collocated with the ASME 2013 7th International Conference on Energy Sustainability and the ASME 2013 11th International Conference on Fuel Cell Science, Engineering and Technology. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/ht2013-17751.
Повний текст джерелаАнотація:
A numerical phase field model is developed to investigate the Rayleigh-Taylor instability (RTI) subject to a horizontal electric field. The model entails the simultaneous solution of the electric field equation and the Navier-Stokes equation for fluid flow coupled with the phase field model for the evolution of the fluid-fluid interface deformation and morphology. The in-house Fortran code was developed to enable the computing. Results show that, for pure dielectric fluids, the presence of the horizontal electric field induces polarization charges and produces a Korteweg-Helmholtz force which acts to suppress the RTI. For poorly conducting liquids, for which a leaky dielectric description is more appropriate. In this model, both polarization and free charges present. The effect of the free charge in this case depends on the specific values of λε and λσ. For the fluids of λε >1, it aggravates RTI if λσ<λε, and suppresses that when λσ>λε.
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Gu, Claire, and Pochi Yeh. "Scattering due to random space-charge field in photorefractive crystals." In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/oam.1991.mj6.
Повний текст джерелаАнотація:
The fluctuation of refractive index introduced by the random space-charge field via the Pockels effect is one of the noise sources in photorefractive media. In EO crystals, including photorefractive crystals, charge particles such as ionized dopants and defects are randomly distributed. The space-charge electric field generated by these charge particles induces a fluctuation in dielectric constant (or equivalently index of refraction) from the Pockels effect. Such fluctuation exists even in the presence of hologram recording and two-wave mixing. When the crystal is illuminated by light, scattering occurs in a manner similar to that of Rayleigh scattering. This kind of scattering exists in all photorefractive crystals, where ionized dopants and/or defects are responsible for the formation of index gratings. Such scattering leads to statistical noise in photorefractive devices. In this paper, we consider the scattering from randomly distributed charge particles in photorefractive crystals. The scattering cross section is analyzed in terms of the fluctuation of refractive index induced by the random space-charge field via Pockels effect. We also discuss the noise due to scattering from these noisy index gratings. The signal to noise ratio and the minimum modulation depth for an index grating are discussed. The analysis can be extended to cover all EO media.
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Borisov, A. B., X. Shi, O. B. Shiyaev, A. McPherson, K. Boyer, C. K. Rhodes, V. V. Korobkin, and V. Karpov. "Optimization of Self-Channeling of Relativistically Intense Laser Beams in Underdense Plasmas." In Shortwavelength V: Physics with Intense Laser Pulses. Washington, D.C.: Optica Publishing Group, 1993. http://dx.doi.org/10.1364/swv.1993.puip50.
Повний текст джерелаАнотація:
Self-channeling of high power subpicosecond ultraviolet (248 nm) laser pulses has been observed experimentally in various high pressure gases. The propagation zone was observed to be approximately 2 µm in diameter and 3 mm in length, a distance of about 100 Rayleigh ranges. Theoretical modeling of relativistic and charge- displacement self-channeling of laser pulses in plasmas with our experimental parameters yield results which are in qualitative agreement with the experimental observations.