Academic literature on the topic 'Wall Nucleation'
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Journal articles on the topic "Wall Nucleation"
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de Campos, Marcos Flavio, and José Adilson de Castro. "The Critical Volume for Nucleation." Materials Science Forum 660-661 (October 2010): 279–83. http://dx.doi.org/10.4028/www.scientific.net/msf.660-661.279.
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In magnets based in phases with high magnetocrystalline anisotropy like Nd2Fe14B or SmCo5 there is a competition between magnetostatic energy and domain wall energies. If the grain size is large, the formation of domain walls is energetically favorable. When the formation of domain walls is an unfavorable process, coercivity is larger. A better comprehension of this phenomenon is possible if the energy necessary for the first domain wall formation is properly evaluated. To address this problem, the magnetostatic energy of a sphere magnetized in two opposite directions, separated by a domain wall, is calculated using Legendre Polynomials. The data allow the determination of the reversible volume for nucleation. It is predicted a “recoil effect”, the magnetization may be reversible until a given volume of reverse magnetization.
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Osuna Ruiz, D., O. Alejos, V. Raposo, and E. Martínez. "Geometrical design for pure current-driven domain wall nucleation and shifting." Applied Physics Letters 121, no. 10 (September 5, 2022): 102403. http://dx.doi.org/10.1063/5.0106689.
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Nucleation of domain walls by current-driving a single domain wall, confined to the junction area of two symmetrical strips, is investigated using systematic micromagnetic simulations. Secondary domain walls (equivalently, bits encoded in domains) are simultaneously nucleated and driven by alternatively applying current pulses between two terminals in the structure. Simulations show that nanosecond-duration current pulses nucleate and drive series of robust up/down domains even under realistic conditions. These results demonstrate a technique for sequentially nucleating and shifting domain walls without using attached external “bit lines,” fields, or modifying the ferromagnetic strip.
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Kondo, Seishi. "Quantum nucleation on a wall." Physica B: Condensed Matter 329-333 (May 2003): 384–85. http://dx.doi.org/10.1016/s0921-4526(02)02134-8.
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Ehrhart, S., and J. Curtius. "Influence of aerosol lifetime on the interpretation of nucleation experiments with respect to the first nucleation theorem." Atmospheric Chemistry and Physics 13, no. 22 (November 26, 2013): 11465–71. http://dx.doi.org/10.5194/acp-13-11465-2013.
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Abstract. The SAWNUC (Sulphuric Acid Water NUCleation) microphysical aerosol nucleation model is used to study the effect of reactor walls on the interpretation of nucleation experiments with respect to nucleation theory. This work shows that loss processes, such as wall losses, influence the interpretation of nucleation experiments, especially at low growth rates and short lifetimes of freshly nucleated particles. In these cases the power dependency of the formation rates, determined at a certain particle size, with respect to H2SO4 does not correspond to the approximate number of H2SO4 molecules in the critical cluster as expected by the first nucleation theorem. Observed ∂log(J)/∂log([H2SO4]) therefore can vary widely for identical nucleation conditions but different sink terms.
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He, X., E. K. H. Salje, X. Ding, and J. Sun. "Immobile defects in ferroelastic walls: Wall nucleation at defect sites." Applied Physics Letters 112, no. 9 (February 26, 2018): 092904. http://dx.doi.org/10.1063/1.5021542.
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Hadikhani, Pooria, S. Mohammad H. Hashemi, Steven A. Schenk, and Demetri Psaltis. "A membrane-less electrolyzer with porous walls for high throughput and pure hydrogen production." Sustainable Energy & Fuels 5, no. 9 (2021): 2419–32. http://dx.doi.org/10.1039/d1se00255d.
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Ehrhart, S., and J. Curtius. "Influence of aerosol lifetime on the interpretation of nucleation experiments with respect to the first nucleation theorem." Atmospheric Chemistry and Physics Discussions 13, no. 4 (April 12, 2013): 9733–50. http://dx.doi.org/10.5194/acpd-13-9733-2013.
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Abstract. The SAWNUC microphysical aerosol nucleation model is used to study the effect of reactor walls on the interpretation of nucleation experiments with respect to nucleation theory. This work shows that loss processes, such as wall losses, influence the interpretation of nucleation experiments, especially at low growth rates and short lifetime of freshly nucleated particles. In these cases the power dependency of the formation rates, determined at a certain particle size, with respect to H2SO4 does not correspond to the approximate number of H2SO4 molecules in the critical cluster as expected by the first nucleation theorem. Observed ∂log(J)/∂log([H2SO4]) therefore can vary widely for identical nucleation conditions but different sink terms.
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Shen, Fanyi, Rongfu Gao, Wenji Liu, Wenjie Zhang, and Qi Zhao. "421 Thermodynamic Analysis on Mechanism of Deep Supercooling of Tissue Water in Winter-hardy Plants." HortScience 35, no. 3 (June 2000): 465F—466. http://dx.doi.org/10.21273/hortsci.35.3.465f.
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It is known that the redistribution of water and the formation of dispersed water units appears to be a prerequisite for deep supercooling. A concentration of the cell solute results from the migration of water during extracelullar freezing and lowers the temperature of homogeneous nucleation, but we are convinced that nucleation of ice within cells may be initiated by a heterogeneous mechanism, except we consider a small spherical cave, the water can freeze on the wall of this cave. We are also convinced that the solid walls of the capillary exert an external potential on the water molecules, causing the shift of the triple point of the confined fluids. Based on Fletcher's work for spherical particle, we have gotten the formula of critical free energy in the process of heterogeneous nucleation of water in a small spherical cave. This presentation introduces the theoretical background and counts the drop of temperature in heterogeneous nucleation. Then, putting two actions (depression of triple point and process of heterogeneous nucleation) together, we have calculated the freezing point. Sometimes it is lower than –38 °C. Some phenomena can be explained by using this theory: 1) Water is at the tension status, which means that it wets plant tissue, so the triple point (melting point) of tissue water can be lowered. 2) The redistribution of water, formation of dispersed water units, and dry region preventing ice from propagating, all allow heterogeneous nucleation, then the two actions can be synthesized and the water would lead to deep supercooling. If the barriers were destroyed, heterogeneous nucleation and deep supercooling would certainly be lost. 3) This theory is only suited to rigid wall of small cave, so we understand why cell wall rigidity has been shown to affect freezing characteristics. Project 39870234 supported by National Nature Science Foundation.
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Winkler, S., W. Reim, and K. Schuster. "Domain nucleation and wall movement in TbFeCo." Thin Solid Films 175 (August 1989): 265–71. http://dx.doi.org/10.1016/0040-6090(89)90838-9.
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Skomski, R., T. A. George, and D. J. Sellmyer. "Nucleation and wall motion in graded media." Journal of Applied Physics 103, no. 7 (April 2008): 07F531. http://dx.doi.org/10.1063/1.2835483.
Full textDissertations / Theses on the topic "Wall Nucleation"
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Trapp, Beatrix. "Nucleation and propagation of magnetic domain walls in cylindrical nanowires with diameter modulations." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAY011.
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Dans les dispositifs actuels de sauvegarde de données, les bits d'informations sont stockées sous la forme de paroi de domaines dans une couche mince, voire des media "patternés". Le support reste donc 2D. De nos jours, la densité de stockage tend vers une valeur maximale qu'il est difficile de dépasser pour des raisons fondamentales et technologiques. Ainsi, récemment des efforts ont été réalisés pour développer des dispositifs 3D qui allient la polyvalence de la mémoire RAM solide avec un coût comparable à celui des disques durs actuels.Un nouveau concept théorique particulièrement intéressant pour une mémoire magnétique en 3D a été proposé en 2004 par S. Parkin et al.. Cette mémoire de type registre à décalage est constituée d'un réseau de nanofils magnétiques verticaux avec une section transversale cylindrique ou bien rectangulaire. Dans ce nouveau type de mémoire, les bits sont codés sous forme d'une série de parois de domaine. Cette dernière peut être déplacée vers une tête de lecture intégrée par des impulsions de courant polarisé en spin de quelques nanosecondes.Les parois de domaines magnétiques dans des nanofils cylindriques ont suscité l'intérêt de la communauté scientifique en raison de leur application possible dans un dispositif fonctionnel ainsi qu'en raison de nouvelles propriétés intéressantes qui résultent du confinement géométrique des parois. A ce jour, seules quelques études expérimentales sur de telles parois de domaines existent. Elles ont mis en évidence la difficulté de maîtriser la propagation de parois dues à des forts effets de piégeage. Jusqu'à présent, l'origine microscopique de ce piégeage n'a été que partiellement comprise. On s'attend à ce qu’indépendamment de la qualité géométrique du fil, la microstructure du matériau puisse jouer un rôle non négligeable.Dans le cadre du projet européen FP7 m3D, l'objectif de mon travail de thèse a été d'étudier la propagation des parois de domaine dans des nanofils cylindriques avec des modulations de diamètre. L'énergie de ces parois de domaine augmentant avec le diamètre du fil, on s'attend à ce que des excroissances (ou des constrictions) agissent comme des barrières d'énergie artificielles (respectivement puits). Par conséquent, une propagation de paroi de domaine contrôlée via la géométrie du fil semble possible.La première partie de mon travail concerne l'optimisation des matériaux. Des fils d'un alliage de NiCo (diamètre de 100-200nm et longueur de plusieurs dizaines de micromètres) avec deux géométries distinctes ont été fabriqués par électrodéposition en collaboration avec le groupe du Prof. J. Bachmann à l' Université d'Erlangen. Pour chaque géométrie, j'ai exploré l'effet de la composition de l'alliage ainsi que d'un recuit sur la microstructure du matériau. Par la suite, la propagation des parois de domaine dans des nanofils individuels a été étudiée sous l'influence d'un champ magnétique quasi-statique ou d'une impulsion de champ magnétique avec une durée d'impulsion de l'ordre de la nanoseconde. Dans la dernière partie de ma thèse, j'ai effectué des simulations micromagnétiques complémentaires pour étudier l'effet de la géométrie des modulations sur le piégeage de ces parois de domaine magnétiquesIn all current data storage devices, the information bits are stored in form of domain walls in a thin film or in patterned media on a two-dimensional surface . Within the next decade, further increase of the storage density in these devices is expected to come to a halt due to several fundamental and technological issues. Thus there have recently been efforts to develop three-dimensional devices combining the versatility of solid state RAM with the cost efficiency of common hard disk drives.A particularly interesting theoretical concept for a three-dimensional magnetic memory has been proposed in 2004 by S. Parkin et al. . Their racetrack memory consists of a vertical array of magnetic nanowires with either cylindrical or rectangular cross section. The bits are encoded in a series of up to 100 domain walls per wire. Using nanosecond spin polarized current pulses these walls are shifted past an integrated read head.Magnetic domain walls in cylindrical nanowires have raised the interest of the scientific community due to their possible application in a functional device as well as due to exciting new properties which arise from the geometric confinement. Up to date, only a few pioneering experimental studies on such domain walls exist. They indicate strong pinning effects preventing a deterministic domain wall propagation. So far the microscopic origin of this pinning has only partially been understood. It is expected however that beside the wire geometry the material microstructure may play a considerable role.Situated within the framework of the European FP 7 project m3D, the objective of my work has been to investigate the domain wall propagation in cylindrical nanowires with diameter modulations by means of magnetic force microscopy and micromagnetic simulation. As the domain wall energy increases with the wire diameter, protrusions (resp. notches) are expected to act as an artificial energy barrier (resp. well). Consequently, a deterministic domain wall propagation controlled via the wire geometry seems possible.A first part of my work concerns material optimization. For this, NiCo alloy wires (100-200nm diameter and multiple tens of micrometers in length) with two distinct geometries have been fabricated by template assisted electrodeposition (Chemist collaborators at Univ. Erlangen, Prof. J.Bachmann). I have then explored the impact of the alloy composition as well as of possible post-fabrication annealing on the material microstructure. Subsequently, domain wall propagation in individual nanowires has been investigated under the influence of either a quasistatic magnetic field or a nanosecond magnetic field pulse. In addition I have performed complementary micromagnetic simulations to study the effect of the modulation geometry on the domain wall pinning
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Bryan, Matthew Thomas. "Nucleation and propagation of domain walls in Permalloy nanostructures." Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.490331.
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Borie, Benjamin [Verfasser]. "The propagation and nucleation of magnetic domain walls in multi-turn counter sensor devices / Benjamin Borie." Mainz : Universitätsbibliothek Mainz, 2018. http://d-nb.info/1162300396/34.
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González, Oyarce Aníbal Lautaro. "360° domain walls : nucleation mechanisms during thin film switching, and their application to high density non-volatile memory." Thesis, University of Cambridge, 2014. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708186.
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Mangin, Stéphane. "Nucléation et propagation d'une paroi dans une nanostructure magnétique : la jonction à paroi de domaines." Université Joseph Fourier (Grenoble ; 1971-2015), 1997. http://www.theses.fr/1997GRE10085.
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Afin d'etudier la nucleation et la propagation de parois de domaines magnetiques a 180 a travers une barriere de potentiel, nous avons prepare des echantillons constitues d'une fine couche de tbfe amorphe comprise entre deux couches de gdfe amorphe. Les couches de gdfe ont des epaisseurs differentes (typiquement 500a et 1000a) afin de permettre la nucleation d'une paroi dans seulement une des couches. De plus, nous avons induit une anisotropie uniaxiale dans le plan de l'echantillon, necessaire a la formation de parois a 180. Le gdfe presentant une constante anisotropie beaucoup plus faible que le tbfe, ce dernier agit donc pour une paroi comme une barriere de potentiel. Dans notre etude l'epaisseur de tbfe est comprise entre 2 et 20a. Ces nanostructures magnetiques sont similaires aux jonctions a parois de domaine imaginees dans une approche theorique. Les mesures d'aimantation quasi-statiques ont montre qu'apres nucleation d'une paroi de plusieurs centaines d'angstroms, la paroi se comprime sur la couche de tbfe avant de la traverser. La propagation a lieu pour un champ dependant de la temperature de mesure, ce qui est accord avec le modele de traversee de barriere par activation thermique. Des mesures de relaxation de l'aimantation ont permis d'etudier les phenomenes d'activation thermique et de montrer l'influence du champ et de l'epaisseur de tbfe sur la forme de la barriere. Une distribution de hauteur de barriere quasiment nulle de hauteur de barriere en a ete deduite. Enfin, des mesures dynamiques, locales a basse temperature par technique micro-squid ont permis d'etudier les renversements de l'aimantation (nucleation et propagation). Nous avons pu observer en dessous de 0. 7 k un processus d'activation different de celui observe par relaxation, qui pourrait etre une manifestation de l'effet tunnel de paroi prevu theoriquement.
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Guang-FuWang and 王洸富. "Screen charge effect on nucleation dynamics of 180-degree domain wall." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/25413431595313384929.
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碩士國立成功大學
物理學系碩博士班
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In this study, I present a quantitative study of the 180 degree domain wall motion in epitaxial BiFeO3 films, and discuss the domain growth behaviors by the piezoresponse force microscopy (PFM). The topography, in-plane (IP), and out-of-plane (OP) components of domains for BFO thin films can be revealed simultaneously. The upward and downward activation field (αup and αdown) on BFO(001)/SRO/STO epitaxial thin film was about 2.601~ 2.895 MV/cm and 0.889~ 0.947 MV/cm, respectively. We suggest the as-grown 710 domain wall only had clip effects on dynamic behaviors of the domains. When the domain grew to the size about original domain width, the domain wall was clipped by the 710 domain wall. . In order to understand the polarization axis and the thickness effect under the dynamic process, we used two different samples, BFO(111)/SRO/STO and BFO(001)/SRO/DSO thin films. Finally, we created a screen charge model to support the activation behavior. The static electricity energy plays a critical role in the activation process.
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"Nucleation and Growth of Single Layer Graphene on Supported Cu Catalysts by Cold Wall Chemical Vapor Deposition." Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.50114.
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abstract: Chemical Vapor Deposition (CVD) is the most widely used method to grow large-scale single layer graphene. However, a systematic experimental study of the relationship between growth parameters and graphene film morphology, especially in the industrially preferred cold wall CVD, has not been undertaken previously. This research endeavored to address this and provide comprehensive insight into the growth physics of graphene on supported solid and liquid Cu films using cold wall CVD.
A multi-chamber UHV system was customized and transformed into a cold wall CVD system to perform experiments. The versatile growth process was completely custom-automated by controlling the process parameters with LabVIEW. Graphene growth was explored on solid electrodeposited, recrystallized and thin sputter deposited Cu films as well as on liquid Cu supported on W/Mo refractory substrates under ambient pressure using Ar, H₂ and CH₄ mixtures.
The results indicate that graphene grown on Cu films using cold wall CVD follows a classical two-dimensional nucleation and growth mechanism. The nucleation density decreases and average size of graphene crystallites increases with increasing dilution of the CH₄/H₂ mixture by Ar, decrease in total flow rate and decrease in CH₄:H₂ ratio at a fixed substrate temperature and chamber pressure. Thus, the resulting morphological changes correspond with those that would be expected if the precursor deposition rate was varied at a fixed substrate temperature for physical deposition using thermal evaporation. The evolution of graphene crystallite boundary morphology with decreasing effective C deposition rate indicates the effect of edge diffusion of C atoms along the crystallite boundaries, in addition to H₂ etching, on graphene crystallite shape.
The roles of temperature gradient, chamber pressure and rapid thermal heating in C precursor-rich environment on graphene growth morphology on thin sputtered Cu films were explained. The growth mechanisms of graphene on substrates annealed under reducing and non-reducing environment were explained from the scaling functions of graphene island size distribution in the pre-coalescence regime. It is anticipated that applying the pre-coalescence size distribution method presented in this work to other 2D material systems may be useful for elucidating atomistic mechanisms of film growth that are otherwise difficult to obtain.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2018
Books on the topic "Wall Nucleation"
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Karapetrov, G., S. A. Moore, and M. Iavarone. Mesoscopic Effects in Superconductor–Ferromagnet Hybrids. Edited by A. V. Narlikar. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780198738169.013.8.
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This article examines the occurrence of mesoscopic effects in superconductor-ferromagnet hybrids. It begins with an overview of theories underpinning superconducting/ferromagnetic (S/F) hybrid structures, focusing on their vortex nucleation conditions and vortex behavior as well as the localized nucleation of superconductivity in an ideal S/F system. It then presents experimental measurements of the localized superconducting state in the cases of domain wall and reverse domain superconductivity, along with the vortex state in planar S/F hybrids. In particular, it considers nucleation thresholds for superconducting vortices and equilibrium vortex configurations. Finally, it discusses the results of local scanning probe measurements of the novel mesoscopic effects that emerge in magnetically coupled S/F hybrid structures in the absence of proximity effects.
Book chapters on the topic "Wall Nucleation"
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Bertelsmann, Anne, and Richard H. Heist. "How does the wall of the diffusion cloud chamber affect performance?" In Nucleation and Atmospheric Aerosols 1996, 199–202. Elsevier, 1996. http://dx.doi.org/10.1016/b978-008042030-1/50047-0.
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Ievlev, A. V., A. Tselev, R. Vasudevan, S. V. Kalinin, A. Morozovska, and P. Maksymovych. "Nanoscale Ferroelectric Switching: A Method to Inject and Study Non-equilibrium Domain Walls." In Domain Walls, 245–70. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198862499.003.0011.
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This chapter focuses on the electric field-induced formation of a single nanoscale polarization domain, emphasizing that nucleation, growth, and annihilation of such a domain enables injection of non-equilibrium domain walls. The focus on nanoscale domains is motivated in large part by advances in scanning probe microscopy (SPM), where the ever-increasing drive to improve spatial resolution was met by a natural reduction of the size of one of the electrodes in a ferroelectric capacitor down to nanoscale dimensions. In this case, the process of ferroelectric switching becomes dominated by the nucleation of a single domain of the opposite polarization. Once allowed to equilibrate, the end-result of the single-domain switching is injection of a new domain wall(s) into the original ferroelectric volume. Likewise, reversing the polarization under the probe will in general eliminate the domain wall(s). The nanoscale ferroelectric switching becomes, therefore, an efficient approach to inject and erase DWs on-demand. However, its primary value may be in facilitation of detailed understanding of the DW injection mechanisms as well as investigation of the range of possible DW configurations, that can be injected up to the highest fields achievable in a given material.
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González Solórzano, María-Guadalupe, Rodolfo Morales-Dávila, Jafeth Rodríguez Ávila, Carlos Rodrigo Muñiz-Valdés, and Alfonso Nájera Bastida. "The Physical Chemistry of Steel Deoxidation and Nozzle Clogging in Continuous Casting." In Casting Processes and Modelling of Metallic Materials. IntechOpen, 2021. http://dx.doi.org/10.5772/intechopen.95369.
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Nozzle clogging in continuous casting of steel originates by the adherence of alumina particles and other oxides, precipitated during the liquid steel deoxidation, on the refractory material’s surface. Hence, these particles’ nucleation and growth rates in supersaturated melts are analyzed considering, specifically, the role of the interfacial tensions between alumina, silica, and other oxides and the liquid metal. Weak steel deoxidizers like silicon do not need high supersaturations favoring high nucleation rates, giving particles’ narrow size distributions thanks to fast diffusion and Ostwald-ripening coagulation. Strong deoxidizers, like aluminum, need high supersaturation levels leading to broad size distributions. Besides, the morphology of these particles depends on the nucleation and growth mechanisms. The adhesion forces among the deoxidation particles, forming clusters, depending on the morphology and the oxide’s chemistry. The stability of the nozzle’s clog, adhered to the nozzle’s wall, depends on the interface tensions between the melt and the nozzle’s refractory surface and between the melt and the inclusion. The results obtained here help set up basic recommendations in steel refining and materials specifications of casting nozzles.
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Yudin, P. V., and L. J. McGilly. "Control of Ferroelectric Domain Wall Motion using Electrodes with Limited Conductivity." In Domain Walls, 293–310. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780198862499.003.0013.
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This chapter addresses the experimental control of ferroelectric DW motion in thin films using electron-beam induced deposition (EBID) electrodes with limited conductivity which governs the supply of charges required for DW nucleation and propagation. The problem of a moving domain boundary, addressed in this chapter, belongs to the general class of free-boundary problems, or Stefan problems, after Josef Stefan who mathematically described ice formation and then demonstrated generality of his approach by applying the same technique to describe diffusion. In the frame of this approach the position of the boundary is determined from the transport of a physical quantity, flowing through and partially consumed at the boundary. Nowadays mathematical modelling of Stefan problems has developed into a rich field of knowledge where both analytical and numerical methods are applied to solve various important applied tasks. In this chapter, the process is described by analogy to the classical Stefan model, historically applied to the motion of phase boundaries under propagation of heat but which is here applied to precisely describe DW motion under linear electrodes and the 2D growth of a circular domain.
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Pawlikowski, Maciej. "Minerals in Human Blood Vessels and Their Dissolution in Vitro." In Geology and Health. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195162042.003.0033.
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Cardiovascular disease knows no ethnic, national, or geographic boundaries. Men and women throughout the world can become affected by the obstruction of their arteries by cholesterol and the mineral hydroxylapatite (HA).This complex process leads to dysfunction of the arterial system and, because of the necessity of circulation of oxygenated blood, it also affects many tissues and organs. The whole process of occlusion (mineralization of the blood vessels), including precipitation and inorganic crystal formation, takes place in stages. The first stages are thought to involve cholesterol deposits (atherosclerotic plaque formation) in the interior of the vessel walls, or “intima,” as it is known. The formation of hydroylapatite, or “calcification,” begins with the attraction and localization of ions, mainly Ca2+ and PO43+, within the arteries. The vessels become altered and lose their suppleness, effectively interfering with their function as conduits for the blood (Pawlikowski 1986, 1991a,b, 1993, Pawlikowski et al. 1994). The initial stages of deposition can be detected with sensitive physical and chemical methods in vivo and with traditional laboratory methods and techniques on excised samples. In the mineralization stage, grains and crystals may become visible on heart valves as well as in the aortic tissue. (Pawlikowski and Pfitzner 1995,1999), and the new compounds can be identified using scanning electron microscopy and X-ray diffraction. Reasons for the destruction of tissues and the nucleation of minerals can be attributed to allodefects and autodefects. Autodefects in vessels are those attributable to abnormalities in the component tissues in the wall or pre-existing physical conditions. For example, at arterial bifurcations, intense local trauma from the flowing blood fluid might cause changes in those regions and attract cirulating ions. Autodefects are the result of reactions between biological tissues and foreign materials, such as small particles (dust) of all sorts, including bacteria or minerals that have been inhaled and travelled from the lungs via the blood into vessels throughout the body. Alternatively, allodefects may arise from poisons produced by bacteria and viruses during infections, or by other and various chemical products, such as food preservatives, that might be part of the circulating blood.
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Gravner, Janko. "Growth Phenomena in Cellular Automata." In New Constructions in Cellular Automata. Oxford University Press, 2003. http://dx.doi.org/10.1093/oso/9780195137170.003.0010.
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We illustrate growth phenomena in two-dimensional cellular automata (CA) by four case studies. The first CA, which we call Obstacle Course, describes the effect that obstacles have on such features of simple growth models as linear expansion and coherent asymptotic shape. Our next CA is random-walk-based Internal Diffusion Limited Aggregation, which spreads sublinearly, but with a shape which can be explicitly computed due to hydrodynamic effects. Then we propose a simple scheme for characterizing CA according to their growth properties, as indicated by two Larger than Life examples. Finally, a very simple case of Spatial Prisoner’s Dilemma illustrates nucleation analysis of CA. In essence, analysis of growth models is an attempt to study properties of physical systems far from equilibrium (e.g., Meakin [34] and more than 1300 references cited in the latter). Cellular automata (CA) growth models, by virtue of their simplicity and amenability to computer experimentation [25], have become particularly popular in the last 20 years, especially in physics research literature [40, 42]. Needless to say, precise mathematical results are hard to come by, and many basic questions remain completely open at the rigorous level. The purpose of this chapter, then, is to outline some successes of the mathematical approach and to identify some fundamental difficulties. We will mainly address three themes which can be summarized by the terms: aggregation, nucleation, and constraint-expansion transition. These themes also provide opportunities to touch on the roles of randomness, monotonicity, and linearity in CA investigations. We choose to illustrate these issues by particular CA rules, with little attempt to formulate a general theory. Simplicity is often, and rightly, touted as an important selling point of cellular automata. We have, therefore, tried to choose the simplest models which, while being amenable to some mathematical analysis, raise a host of intriguing unanswered questions. The next few paragraphs outline subsequent sections of this chapter. Aggregation models typically study properties of growth from a small initial seed. Arguably, the simplest dynamics are obtained by adding sites on the boundary in a uniform fashion.
Conference papers on the topic "Wall Nucleation"
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Lu, J. F., and X. F. Peng. "Microscopic Activation Phenomena in Heterogeneous Nucleation." In ASME 2003 Heat Transfer Summer Conference. ASMEDC, 2003. http://dx.doi.org/10.1115/ht2003-47469.
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The energy property in liquid near the wall was theoretically investigated to understand the effects of wall surface on inception process of nucleation or embryo bubble formation in boiling systems. Analyses indicate that the liquid near heating wall has higher pressure than in bulk region owing to existence of strong attractive forces, and this pressure could maintain a stable liquid microlayer and cause a steady energy peak near the wall. So a vapor embryo is likely to occur beyond the stable microlayer instead of exactly at the solid surface. The stable liquid layer may also be the inception structure of the ultrathin film before nucleation occurs. Fluctuations enhance the phenomenon of energy peak until the nucleation occurs, while energy peak promotes nucleation. Employing the concept of energy peak, the inception phenomena of the microlayer and the formation of embryo bubbles near solid surface were described.
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Johnston, Joseph, and R. Panneer Selvam. "Molecular Dynamics Simulation of Vapor Bubble Nucleation in 2D Lennard-Jones Fluid Along Nanometer-Sized Cavities." In ASME/JSME 2011 8th Thermal Engineering Joint Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/ajtec2011-44188.
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Heterogeneous vapor bubble nucleation was numerically simulated on surfaces containing nanometer-sized rectangular cavities of various sizes (ranging from 2.72–9.36 nm width & 4.09–8.34 nm depth). Non-equilibrium molecular dynamics simulations at constant wall temperature were carried out for the two-dimensional (2D) Lennard-Jones (LJ) fluid which was in thermal contact with LJ solid wall. Nucleation was induced by expanding the system volume to a metastable state while keeping the temperature of the solid wall constant. When the aspect ratio (depth-to-width) of the cavity was large (∼3-to-1), the nucleation rate was increased nearly three-fold compared to the flat surface for relatively large wettability; however, the nucleation rate was nearly the same for lower wettability surfaces. Nucleation was generally favored within the cavities due to the stabilization of the cavity side-walls. The value of cutoff radius, wall temperature, and solid-liquid wettability was varied to determine their effect on nucleation rate. The 2D model was validated by comparing thermodynamic averages of pressure and potential energy to predicted values from a 2D LJ equation of state.
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Tian, Y., X. D. Wang, and X. F. Peng. "Characteristics of Earlier Nucleation for Boiling in Microchannels." In ASME 2004 2nd International Conference on Microchannels and Minichannels. ASMEDC, 2004. http://dx.doi.org/10.1115/icmm2004-2386.
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In this study, the nucleus formation and bubble growth at beginning of boiling process in microchannels was investigated. Canonical molecular distribution was introduced to analyze characteristics of nucleate boiling when liquid molecular number is very small. The minimum bulk phase volume in which phase change was enable to occur was determined from thermodynamic theory of bubble formation in a superheated liquid and from the energy distribution of the molecules in the bulk phase at a given temperature and pressure. The comparison of the free energy decrease during nucleus formation on a flat wall and at a corner of walls indicates that nuclei more easily form at a corner than on a flat wall for wetting liquids. The experimental results demonstrated that the superheat temperature increased as diameter of microchannels decreased. The experimental measurements are in a quite agreement with theoretical predictions.
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Bai, Bofeng, and Sijie Li. "Vapor Embryo Nucleation in Near-Wall Region Under Pool Boiling Conditions." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-22142.
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To construct a model of the microscopic near-wall region in a macroscopic pool boiling system, the present work introduced the effect of the solid wall at the bottom of the simulation system and the infinite liquid region outside it as extra potential. Molecular dynamics simulation results showed that thermodynamics properties of near-wall region was influenced by the interaction strength and deviated from the bulk liquid region. Vapor embryo nucleated at a position several nanometers away from the solid surface. With the increase of Hamaker constant, the vapor embryo occurred at a position farther away from the solid wall.
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Chen, Weihong, Ang Guo, and Lixin Yang. "Experimental Investigation of Wall Nucleate Boiling Models in Narrow Channel." In 2013 21st International Conference on Nuclear Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/icone21-16579.
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Using deionized water as working medium, studies on visualization of the behavior of subcooled boiling bubbles in narrow rectangular channels have been conducted at atmospheric pressure, with the help of a high-speed digital camera. The effects of wall superheat, fluid subcooling and mass flux on the bubble dynamic model of nucleation site density, bubble departure frequency and bubble departure diameter were investigated. This paper analyzed the visual graphic results and obtained quantitative values about bubble nucleation site density, bubble departure frequency and bubble departure diameter under different conditions. Based on the results, wall nucleate boiling models in the conventional channel put forward by Nilanjana Basu have been corrected. The new correlation agrees reasonably well with existing experimental data in 2mm narrow rectangular channel.
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Berkeley, Pamela, and Van P. Carey. "Thermodynamic Analysis of Wall Effects on Phase Stability and Homogeneous Nucleation in Nanotubes Containing Superheated Liquid." In ASME 2008 6th International Conference on Nanochannels, Microchannels, and Minichannels. ASMEDC, 2008. http://dx.doi.org/10.1115/icnmm2008-62337.
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Rapid heating or sudden depressurization can create highly superheated liquid conditions in stationary or flowing liquid in nanochannels. In these situations, the phase stability of the liquid and the conditions for the onset of bubble nucleation are important factors in the fluid behavior in applications. In the investigation summarized here, a statistical thermodynamics analysis is used to derive a modified version of the Redlich-Kwong fluid property model that accounts for attractive forces between the solid wall surface atoms and liquid molecules in the fluid within a nanochannel. In this model, the wall-fluid attractive forces are quantified in terms of Hamaker constants, which makes it possible to assess the effect of wall-fluid force interactions on the spinodal conditions for a variety of fluid and surface material combinations. This investigation focuses on the application of the aforementioned model to high aspect ratio (parallel plate) channels where a second wall is placed parallel to the first at distances varying in scale from nanometers to micrometers. At large channel widths the fluid properties exhibit wall effects very near each wall with bulk fluid property values being predicted in the center of the channel. As the channel width decreases, the fluid in the center of the channel begins to feel the effects of both walls and the properties deviate from the bulk values throughout the channel; importantly, the spinodal temperature increases significantly above the bulk fluid value. Fluid property profiles are developed for common combinations of walls and fluids, and properties are investigated as a function of non-dimensionalized distance within the channel across various channel widths. The results of this analysis imply that in nano- and micro-passages and near walls with nano-to micro-scale roughness, fluid may experience a stabilizing effect due to its proximity to nearby walls.
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Jiang, Yu Yan, Hiroshi Osada, Masahide Inagaki, and Nariaki Horinouchi. "Wall Thermal Conductivity Effects on Nucleation Site Interaction During Boiling: An Experimental Study." In 2010 14th International Heat Transfer Conference. ASMEDC, 2010. http://dx.doi.org/10.1115/ihtc14-23140.
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The past decades have witnessed the diverse applications of boiling heat transfer enhancement in the removal of high density heat flux released by electronic components or power devices. People have developed many enhanced surfaces to obtain the highest heat transfer coefficient in nucleate boiling or to raise the CHF. In the boiling arena bubbling and nucleation site density play core parts, and hence it is crucial to correlate them quantitatively with surface structure and heat transfer conditions. For example one can determine by that correlation the best arrangement of boiling cavities for a given heat flux. However, the bubbling is highly influenced by inter-bubble actions. It has been found that the interactions can considerably change the bubble’s size, frequency and spatial distribution. The interactions are needed to be taken accounts of for a good correlation. Researchers tried to formulate the interactions as a single function of the inter-site spacing but have obtained contradictory conclusions, as suggests that they depend also on other parameters. In the present study we conducted a saturated boiling heat transfer experiment to investigate the interactions with respects to both the inter-site spacing and the wall thermal conductivity. The test section was fabricated by both copper and stainless steel, whose surface has two cylindrical artificial cavities of 50μm in diameter. It was heated with a uniform heat flux. The results show that both the bubble diameter Db and frequency f are functions of the inter-cavity distance s, but they vary in different manners in the copper and the stainless steel surfaces. In the copper surface, we observed evident enhancement of the boiling heat transfer at 1> S >0.4 and a slight inhibitive effect at 1.6> S >1, where S = s/Db. On the contrary the two nucleate sites in the stainless steel surface interfere with each other giving rise to evident suppression of boiling heat transfer at 1.6> S >0.65 and only slight enhancement at 0.65> S >0.3. Note that the copper’s thermal conductivity is 22 times larger than the stainless steel. Numerical simulation has revealed that the temperature variation beneath the copper cavities is much less than the stainless steel, which partly explains the differences in our experimental results. It is suggested that modeling the bubble interactions should take accounts of not only the distance-to-diameter ratio but also the fluid and wall properties.
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LEE, BUM-HOON, CHUL H. LEE, and WONWOO LEE. "THE NUCLEATION OF THE THICK WALL FOR TOPOLOGICAL INFLATION BY OSCILLATING INSTANTON SOLUTIONS." In Proceedings of the MG13 Meeting on General Relativity. WORLD SCIENTIFIC, 2015. http://dx.doi.org/10.1142/9789814623995_0247.
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Breitkreutz, Stephan, Irina Eichwald, Grazvydas Ziemys, Doris Schmitt-Landsiedel, and Markus Becherer. "Influence of the domain wall nucleation time on the reliability of perpendicular Nanomagnetic Logic." In 2014 IEEE 14th International Conference on Nanotechnology (IEEE-NANO). IEEE, 2014. http://dx.doi.org/10.1109/nano.2014.6968096.
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Stosic, Zoran V., and Vladimir D. Stevanovic. "Multi-Dimensional Numerical Simulation of Burnout on Horizontal Surface in Pool Boiling." In ASME 2002 Joint U.S.-European Fluids Engineering Division Conference. ASMEDC, 2002. http://dx.doi.org/10.1115/fedsm2002-31367.
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Multidimensional numerical simulation of the atmospheric saturated pool boiling is performed under high heat fluxes, near to and at the occurrence of burnout conditions. Heat flux through the vessel bottom wall is varied and its influence on the pool boiling dynamics is analysed. Dynamics of vapour generation on the heating wall is modelled through the density of nucleation sites and the bubble residence time on the wall. The nucleation sites are determined by a random function. The applied numerical grid is able to represent the nucleation sites on the heating wall for both fresh (polished) and aged (rough) heaters at the atmospheric pool boiling conditions. Results are presented for short time period after the initiation of heat supply and vapour generation on the heating surface, as well as for quasi steady-state conditions after two seconds from pool boiling initiation. The results show a replenishment of the heating surface with water and partial surface wetting for lower heat fluxes, while heating surface dry-out is predicted for high heat fluxes. The influence of the density of nucleation sites and the bubble residence time on the wall on the pool boiling dynamics is investigated. Numerical simulations show that decrease of the density of nucleation sites and increase of bubble residence time on the heating surface (characteristics pertinent to fresh-polished heaters) lead to the reduction of critical heat flux values. Obtained results are in excellent agreement with the recent experimental investigations of the upward facing burnout conditions on the horizontal heated plate. Details of the developed numerical procedure are presented. The introduced method of random spatial and temporal generation of the vapour at the heated wall is a new approach. It enables the macroscopic representation of the population of microscopic vapour bubbles, which are generated at nucleation sites on the heater wall, and which burst through liquid micro-layer in thermal-hydraulic conditions close to the burnout. The applied numerical and modelling method has shown robustness by allowing stable calculations for wide ranges of applied modelling boiling parameters (density of nucleation sites and bubble residence time).