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  • Single-molecule diffusion in a periodic potential at a solid-liquid interface

     Skaug, Michael J.; Lacasta Palacio, Ana Maria; Ramirez de La Piscina Millan, Laureano; Sancho Herrero, José María; Lindenberg, Katja; Schwartz, Daniel K.
    Soft matter
    Date of publication: 2014-02-07
    Journal article

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    We used single-molecule tracking experiments to observe the motion of small hydrophobic fluorescent molecules at the interface between water and a solid surface that exhibited periodic chemical patterns. The dynamics were characterized by non-ergodic, continuous time random walk statistics. The step-size distributions displayed enhanced probability of steps to periodic distances, consistent with theoretical predictions for diffusion in an atomic/molecular scale periodic potential. Surprisingly, this general behavior was observed here for surfaces exhibiting characteristic length scales three orders of magnitude larger than atomic/molecular dimensions, and may provide a new way to understand and control solid-liquid interfacial diffusion for molecular targeting applications.

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    Speeding chemical reactions by focusing  Open access

     Lacasta Palacio, Ana Maria; Ramirez de La Piscina Millan, Laureano; Sancho Herrero, José María; Lindenberg, Katja
    Journal of chemical physics
    Date of publication: 2013-04-11
    Journal article

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    We present numerical results for a chemical reaction of colloidal particles which are transported by a laminar fluid and are focused by periodic obstacles in such a way that the two components are well mixed and consequently the chemical reaction is speeded up. The roles of the various system param- eters (diffusion coefficients, reaction rate, and obstacles sizes) are studied. We show that focusing speeds up the reaction from the diffusion limited rate, ~t-1/2 to very close to the perfect mixing rate, ~t1/2~t-1

    We present numerical results for a chemical reaction of colloidal particles which are transported by a laminar fluid and are focused by periodic obstacles in such a way that the two components are well mixed and consequently the chemical reaction is speeded up. The roles of the various system param- eters (diffusion coefficients, reaction rate, and obstacles sizes) are studied. We show that focusing speeds up the reaction from the diffusion limited rate, ~t-1/2 to very close to the perfect mixing rate, ~t1/2~t-1

  • ESTOCASTICIDAD EN SISTEMAS COMPLEJOS NOLINEALES

     Pons Rivero, Antonio Javier; Torrent Serra, Maria Del Carmen; Masoller Alonso, Cristina; Pigolotti, Simone; Ramirez de La Piscina Millan, Laureano; Peñaranda Ayllon, Angelina; Malagarriga Guasch, Daniel; Dies Miracle, Marta; Aragoneses Aguado, Andres; Deza, Juan Ignacio; Garcia Ojalvo, Jorge
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  • Impact of stochastic accelerations on dopant segregation in microgravity semiconductor crystal growth

     Ruiz Martí, Xavier; Bitlloch, Pau; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    Journal of crystal growth
    Date of publication: 2012-09-15
    Journal article

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  • Spatial structure and velocity fluctuations in turbulent bubble jets in microgravity

     Bitlloch, Pau; Ruiz, Xavier; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    International Journal of Transport Phenomena
    Date of publication: 2011
    Journal article

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  • Stochastic g-jitters and directional solidification

     Ruiz, Xavier; Bitlloch, Pau; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    European Low Gravity Research Association Symposium
    Presentation's date: 2011
    Presentation of work at congresses

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  • Interaction between bubbles and turbulence in monodisperse suspensions. Drop tower experiments.

     Bitlloch, Pau; Ruiz, Xavier; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    International Conference on Two-Phase Systems for Ground and Space Applications
    Presentation's date: 2011
    Presentation of work at congresses

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  • Degenerate bifurcations in binary-mixture convection

     Meca Alvarez, Esteban; Mercader Calvo, Maria Isabel; Ramirez de La Piscina Millan, Laureano
    International Symposium Bifurcations and Instabilities in Fluid Dynamics
    Presentation's date: 2011-07-21
    Presentation of work at congresses

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    Characterization of the performance of a minibubble generator in conditions relevant to microgravity  Open access

     Arias Calderón, Santiago; Gonzalez Cinca, Ricardo; Ruiz, X; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    Colloids and surfaces A: physicochemical and engineering aspects
    Date of publication: 2010-08-05
    Journal article

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    We perform a characterization of a recently reported minibubbles (bubbles with a diameter of the order of 10‐3 m) generator in microgravity related conditions. Generation of bubbles is based on the generation of a slug flow in a capillary T‐junction, whose operation is robust to changes in the gravity level. We address questions regarding the performance under different working regimes. In particular, we focus on the regimes found within a large range of gas and liquid injection flow rates. The injection performance is characterized by measuring bubble generation frequency. We propose curves obtained empirically for the behavior of generation frequency and crossover between regimes.

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  • Conective instabilities and directional solidification in binary mixtures

     Meca Alvarez, Esteban
    Defense's date: 2010-06-04
    Department of Applied Physics, Universitat Politècnica de Catalunya
    Theses

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  • Transient convective instabilities in directional solidification

     Meca Alvarez, Esteban; Ramirez de La Piscina Millan, Laureano
    Physics of fluids
    Date of publication: 2010-11-03
    Journal article

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  • DINÁMICA NO LINEAL Y ESTOCÁSTICA EN SISTEMAS FÍSICOS Y BIOFÍSICOS

     Ciudad Alvarez, Aleix; Haurie Ibarra, Laia; Formosa Mitjans, Joan; Lacasta Palacio, Ana Maria; Meca Alvarez, Esteban; Peñaranda Ayllon, Angelina; Ramirez de La Piscina Millan, Laureano
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  • Crystal growth in space: stochastic versus deterministic vibroconvective effects

     Ruiz, Xavier; Bitlloch, Pau; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    Scientific Assembly of the Committee on Space Research
    Presentation's date: 2010
    Presentation of work at congresses

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  • Transient and oscillatory instabilities in directional solidification with solutal convection

     Meca Alvarez, Esteban; Ramirez de La Piscina Millan, Laureano
    Joint SIAM/RSME-SCM-SEMA Meeting Emerging Topics in Dynamical Systems and Partial Differential Equations
    Presentation's date: 2010
    Presentation of work at congresses

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  • Codimension-2 Bifurcations in Binary-Mixture Convection

     Meca Alvarez, Esteban; Mercader Calvo, Maria Isabel; Ramirez de La Piscina Millan, Laureano
    Emerging Topics in Dynamical Systems and Partial Differential Equations
    Presentation's date: 2010-07-01
    Presentation of work at congresses

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  • Transitions between symmetric and non-symmetric flow regimes in a laterally heated binary mixture

     Meca Alvarez, Esteban; Mercader Calvo, Maria Isabel; Ramirez de La Piscina Millan, Laureano
    International Meeting on Thermodiffusion
    Presentation's date: 2010-06-09
    Presentation of work at congresses

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  • Experimental study of a microchannel bubble injector for microgravity applications

     Arias Calderón, Santiago; Ruiz, X; Casademunt Viader, Jaume; Ramirez de La Piscina Millan, Laureano; Gonzalez Cinca, Ricardo
    Microgravity science and technology
    Date of publication: 2009-01
    Journal article

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  • Growth kinetics of nanometric dendrites in metal-carbon thin films

     Corbella, C; Echebarria Dominguez, Blas; Ramirez de La Piscina Millan, Laureano; Pascual, E; Bertran, Enric; González Andujar, José Luis
    Acta materialia
    Date of publication: 2009-10
    Journal article

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    Oscillatory Instabilities in Directional Solidification with Solutal Convection. Transient Regime  Open access

     Meca Alvarez, Esteban; Ramirez de La Piscina Millan, Laureano
    Congreso de Física Estadística
    Presentation's date: 2009-09-11
    Presentation of work at congresses

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    Monodisperse bubble suspensions in turbulent flows in microgravity. Drop Tower experiments  Open access

     Bitlloch, Pau; Ruiz Martí, Xavier; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    Congreso de Física Estadística
    Presentation's date: 2009-09-11
    Presentation of work at congresses

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    Spatial structure and velocity fluctuations in turbulent bubble jets in microgravity  Open access

     Bitlloch, Pau; Ruiz, Xavier; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    Interdisciplinary Transport Phenomena Conference
    Presentation's date: 2009-10-06
    Presentation of work at congresses

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    We study the dynamics of turbulent jets of bubbles created by the injection of a slug flow into a quiescent cavity, both theoretically and experimentally using data from drop tower experiments. The generated bubble jets exhibit a remarkably low degree of coalescence leading to virtually monodisperse suspensions of spherical bubbles. The turbulence of the jet is responsible for the spatial spreading of the bubble distribution in roughly conical jets. We propose a stochastic model for the dispersion of bubbles in the jet, in which the trajectories of individual bubbles can be computed from the stationary solution of a k-epsilon model. Bubble concentration behaves to a good approximation as a passive scalar with a non-homogeneous diffusion. Numerical integration of the model compares well with the experimental data.

  • Solid segregation induced by stochastic acceleration fields

     Bitlloch, Pau; Ruiz, Xavier; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    European Low Gravity Research Association Symposium
    Presentation's date: 2009-09-04
    Presentation of work at congresses

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  • Generation of a Monodisperse Microbubble Jet in Microgravity

     Carrera, J; Ruiz, X; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    AIAA journal
    Date of publication: 2008-08
    Journal article

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  • Characterization of the performance of an injector for the controlled generation of microbubbles

     Arias Calderón, Santiago; Gonzalez Cinca, Ricardo; Ruiz, X; Carrera Ramírez, Jesús; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    59th International Astronautical Congress
    Presentation of work at congresses

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  • Spreading and coalescence of monodisperse bubble suspensions in turbulent jets in microgravity

     Bitlloch, Pau; Ruiz Martí, Xavier; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    International Topical Team Workshop on Two-Phase Systems for Ground and Space Applications
    Presentation's date: 2008-09-12
    Presentation of work at congresses

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  • Characterization of the performance of an injector for the generation of controlled microbubbles

     Arias Calderón, Santiago; Ruiz, X; Ramirez de La Piscina Millan, Laureano; Carrera, J; Casademunt Viader, Jaume; Gonzalez Cinca, Ricardo
    Third International Topical Team Workshop on TWO-PHASE SYSTEMS FOR GROUND AND SPACE APPLICATIONS
    Presentation of work at congresses

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  • Experimental characterization of a microbubble injector

     Arias Calderón, Santiago; Ruiz, X; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume; Gonzalez Cinca, Ricardo
    ELGRA Biennial Symposium and General Assembly
    Presentation of work at congresses

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  • Generation and dynamics of a microbubble jet in microgravity

     Casademunt Viader, Jaume; Carrera, J; Bitlloch, P; Arias Calderón, Santiago; Ruiz, X; Gonzalez Cinca, Ricardo; Ramirez de La Piscina Millan, Laureano; Dreyer, Michael
    3rd International Workshop on Bubble and Drop Interfaces
    Presentation of work at congresses

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    Characterization of a microbubble injector for applications in microgravity  Open access

     Arias Calderón, Santiago; Ruiz, X; Ramirez de La Piscina Millan, Laureano; Carrera, J; Casademunt Viader, Jaume; Gonzalez Cinca, Ricardo
    Experiments in Space and beyond
    Presentation's date: 2007
    Presentation of work at congresses

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  • SISTEMA ENREGISTRAMENT SENYALS BIOMEDICS

     Ramirez de La Piscina Millan, Laureano
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  • Numerical study of the dynamics of a microbubble jet in microgravity

     Bitlloch, P; Carrera, J; Ruiz, X; Gonzalez Cinca, Ricardo; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    3rd International Workshop on Bubble and Drop Interfaces
    Presentation of work at congresses

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  • Dynamics and statistics of a microbubble jet in microgravity

     Bitlloch, P; Ruiz, X; Gonzalez Cinca, Ricardo; Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
    ELGRA Biennial Symposium and General Assembly
    Presentation of work at congresses

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  • Models for solidification dynamics

     Ramirez de La Piscina Millan, Laureano
    Workshop on Patterns: Models and Applications
    Presentation's date: 2007-04-19
    Presentation of work at congresses

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  • Microbubble injector: an experimental quantitative characterization

     Arias Calderón, Santiago; Ruiz, X; Ramirez de La Piscina Millan, Laureano; Carrera, J; Casademunt Viader, Jaume; Gonzalez Cinca, Ricardo
    Third International Symposium on Physical Sciences in Space 2007 (ISPS 2007)
    Presentation of work at congresses

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  • A study of a monodisperse microbubble jet under microgravity conditions

     Carrera, J; Ruiz, X; Bitlloch, P; Ramirez de La Piscina Millan, Laureano; Arias Calderón, Santiago; Gonzalez Cinca, Ricardo; Dreyer, M; Casademunt Viader, Jaume
    Experiments in Space and beyond
    Presentation of work at congresses

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  • Experimental study of a microbubble injector for microgravity applications

     Arias Calderón, Santiago; Ruiz, X; Ramirez de La Piscina Millan, Laureano; Carrera, J; Gonzalez Cinca, Ricardo
    3rd International Workshop on Bubble and Drop Interfaces
    Presentation of work at congresses

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  • ORDEN, RUIDO Y DINÁMICAS EMERGENTES BAJO NOLINEALIDADES

     Ramirez de La Piscina Millan, Laureano; Peñaranda Ayllon, Angelina; Haurie Ibarra, Laia; Meca Alvarez, Esteban; Rodriguez Cantalapiedra, Inmaculada; Lacasta Palacio, Ana Maria; Benitez Iglesias, Raul; Formosa Mitjans, Joan; Gonzalez Cinca, Ricardo; Suñol Galofre, Francesc Xavier; Arias Calderón, Santiago
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  • Desarrollo de Tecnologías de Inyección y Gestión de Burbujas en Microgravedad

     Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
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  • Numerical study of the generation and dispersion of a bubble jet in microgravity

     Bitlloch, P J Carrera; Carrera, J; Ruiz, X; Gonzalez Cinca, Ricardo; Casademunt Viader, Jaume; Ramirez de La Piscina Millan, Laureano
    57th International Astronautical Congress
    Presentation of work at congresses

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  • Avalanches in suspensions of superconducting microgranules

     Peñaranda Ayllon, Angelina; Ramirez de La Piscina Millan, Laureano
    Congreso de Física Estadística
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  • Morpho-hydrodynamical instabilities in directional solidification: transient instabilities

     Meca Alvarez, Esteban; Ramirez de La Piscina Millan, Laureano
    Congreso de Física Estadística
    Presentation of work at congresses

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  • Scaling of avalanche sizes in systems of superheated superconducting spheres

     Peñaranda Ayllon, Angelina; Ramirez de La Piscina Millan, Laureano
    Xarxa temàtica: Nonlinear Dynamics of Spatio-Temporal Selforganization
    Presentation of work at congresses

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  • Spontaneous formation of nanometric multilayers of metal-carbon films by up-hill diffusion during growth

     Corbella, C; Echebarria Dominguez, Blas; Ramirez de La Piscina Millan, Laureano; Pascual, E; González Andujar, José Luis; Bertran, Enric
    Applied physics letters
    Date of publication: 2005-11
    Journal article

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  • Sharp-interface projection of a fluctuating phase-field model

     Benitez Iglesias, Raul; Ramirez de La Piscina Millan, Laureano
    Physical review E: statistical, nonlinear, and soft matter physics
    Date of publication: 2005-06
    Journal article

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  • Bifurcations and chaos in single-roll natural convection with low Prandtl number

     Mercader Calvo, Maria Isabel; Batiste Boleda, Oriol; Ramirez de La Piscina Millan, Laureano; Ruiz, X; Casademunt Viader, Jaume; Rüdiger, S
    Physics of fluids
    Date of publication: 2005-10
    Journal article

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  • Hot-border effects, ordering, and avalanches in planar arrays of superheated superconducting granules

     Peñaranda Ayllon, Angelina; Ramirez de La Piscina Millan, Laureano
    Nuclear instruments and methods in physics research. Section A, accelerators SP
    Date of publication: 2005-03
    Journal article

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  • Phase-field study of transient stages and fluctuations in solidification  Open access

     Benitez Iglesias, Raul
    Defense's date: 2005-01-27
    Department of Applied Physics, Universitat Politècnica de Catalunya
    Theses

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    L'estudi de la formació de microstructures en processos de solidificació té importants aplicacions científiques i tecnològiques. L'aparició d'aquestes estructures determina les propietats elèctriques i mecàniques del material solidificat, i té per tant un important interès tecnològic. La majoria d'aquestes estructures tenen el seu origen en una desestabilització morfològica de la interfase sòlid-líquid que es produeix a mesura que el front avança. Per aquest motiu, l'estudi del comportament dinàmic de la interfase resulta essencial per entendre els mecanismes que intervenen en la creació d'aquests patrons. Els processos de solidificació solen descriure's mitjançant problemes de contorn mòbil. Aquestes formulacions consten d'equacions per a la difusió del calor i de massa en les fases sòlida i líquida, que s'han de resoldre imposant l'acompliment de diverses condicions de contorn mòbils a la interfase. Els problemes de contorn mòbil, malgrat contenir tots els elements que intervenen en la dinàmica i ser de molta utilitat en l'àmbit de l'enginyeria, requereixen un cost computacional que no permet simular sistemes reals en règims interfacials complexos. Els mètodes de camp de fase (phase-field methods), van aparèixer a principis dels anys vuitanta com una eina computacional que permetia l'estudi de fenòmens interfacials de caire general. Aquests mètodes descriuen la forma de la interfase mitjançant un camp continu que pren valors diferents i constants en les dues fases. La dinàmica d'aquest camp és llavors acoblada al camp de difusió de calor o massa que determina l'avanç del front de solidificació. Un dels avantatges d'aquests mètodes és que la seva simulació no requereix d'algorismes de seguiment de la interfase (front tracking algorithsms). És ben conegut que les característiques principals de les microestructures en solidificació, es determinen durant els transitoris inicials en els que els corrents de massa i calor s'adapten a la evolució dinàmica del front. Un dels objectius en aquesta tesi és el de fer servir mètodes de camp de fase per descriure de forma quantitativa aquests transitoris. Per comprovar la validesa del nostre procediment, es realitza una comparació quantitativa entre els resultats numèrics obtinguts i diferents prediccions analítiques derivades del problema de contorn mòbil. Per un altra banda, la desestabilització del front es veu afectada per la presència de fluctuacions al sistema. Aquestes pertorbacions microscòpiques poden tenir el seu origen a les fluctuacions termodinàmiques internes, o bé ser conseqüència de imperfeccions experimentals que actuen com a font externa de soroll. El segon objectiu d'aquesta tesi és la introducció de fluctuacions en mètodes de camp de fase, de forma que es pugui estudiar l'amplificació dinàmica de les pertorbacions microscòpiques que acaben donant lloc a estructures macroscòpiques. Per finalitzar, analitzem el problema de la selecció en solidificació direccional. Estudiem els règims lineal i no-lineal, tot determinant les condicions, el moment i la forma en que apareixen les estructures dendrítiques i cel·lulars.

    Crystal growth is a non-equilibrium process which involves physical mechanisms at very different scales. When a solidification front advances, mass and heat diffusion processes are combined with interfacial phenomena like capillarity or kinetic attachment. A complex interplay between these mechanisms gives rise to complex interfacial structures like snowflakes or cellular patterns. The formation of microstructures in solidification has both a scientific and a technological interest. On one hand, the study of the different interfacial structures constitutes a fundamental problem in the field of non-equilibrium pattern-forming systems. On the other side, from a technological point of view, the presence of microstructures determines the final mechanical and electrical properties of the processed material. Directional solidification is a controlled solidification technique which reproduces the conditions occurring in some important metallurgical processes like material casting or zone melting refining procedures. In a directional solidification experiment, the alloy sample is pulled at a constant velocity towards the cold region of an externally-imposed temperature gradient. Depending on the growth conditions, a morphological destabilization of the solid-liquid interface occurs during early transient stages. These initial transients are associated to a solute redistribution process due to the adaptation of the concentration field to the forced motion of the sample. The main objective of this thesis is to study the dynamical evolution of the morphological deformations of the front from these initial transients to the final stages where the properties of the interfacial pattern are determined. An important point in this process is that the internal fluctuations of the system play the role of an initiation mechanism for the morphological deformations of the front. During the initial transients, some of these microscopic perturbations are amplified by several orders of magnitude, and a range of wavelengths becomes morphologically unstable. The interfacial deformations of the front can be then characterized by means of power spectrum techniques. In order to study the dynamical evolution of the solidification front in directional solidification, we have used both theoretical and computational approaches: The main computational technique used in this thesis is the phase-field approach, which is a powerful method to simulate complex interfacial phenomena. The model equations describe the evolution of a continuous field , which takes different constant values at the solid and liquid bulks of the system. This field is then coupled with equations for the mass diffusion, and allows performing numerical studies without simulating the standard Stefan-like moving boundary problem. The phase-field method provides a diffuse interface description in which the transition from solid to liquid happens in a region of a certain thickness. The interface thickness introduces a new length in the simulations which must be taken into account to recover quantitative results. One major point in this thesis concerns with the introduction of fluctuations in phase-field methods. In the particular case of variational phase-field formulations -in which the model equations can be derived from a single free energy functional for the whole system-, the introduction of fluctuations can be done by applying the Fluctuation-Dissipation theorem. Variational formulations, however, although their appealing structure, present a poor computational efficiency and cannot be used to obtain quantitative results. To this extent, we have derived a general approach which does not relay in the Fluctuation-Dissipation assumption and permits to introduce fluctuations in both variational and non-variational phase-field formulations. Well-established analytical techniques like boundary integral methods for the transient front position and linear stability analysis of the interface during the transient have been used as theoretical predictions for the computational results. The dynamical evolution of the solidification front can be divided in two stages: A linear regime where the initial noise is amplified, and a non-linear coarsening process where the final properties of the interfacial pattern are selected. We have studied these different stages of the solidification process by using the phase-field approach, and good agreement is obtained when comparing with well-established theoretical and experimental predictions.

  • Desarrollo de sistemas de flujos bifasicos en microgravedad

     Ramirez de La Piscina Millan, Laureano; Casademunt Viader, Jaume
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  • Grup de Turbulencia, Fluctuacions i Difusió (Ayuda para grupos de investigación consolidados)

     Ramirez de La Piscina Millan, Laureano; Platonov, Alexei; Carrillo Cortes, Jose Alejandro; Sekula, Emil; Peñaranda Ayllon, Angelina; Echebarria Dominguez, Blas; Auguet Sangra, Carlota Eugenia; Meca Alvarez, Esteban; Cami Babra, Enrique; Castilla Lopez, Roberto; Rodriguez Cantalapiedra, Inmaculada; Grau Barcelo, Joan; Lacasta Palacio, Ana Maria; Redondo Apraiz, Jose Manuel; Sanchez Ariz, Miguel A.; Benitez Iglesias, Raul; Gonzalez Cinca, Ricardo
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  • Dinàmiques no lineals d'autoorganització espai-temporal (2004XT-00013)

     Garcia Ojalvo, Jorge; Auguet Sangra, Carlota Eugenia; Mercader Calvo, Maria Isabel; Ramirez de La Piscina Millan, Laureano; Torrent Serra, Maria Del Carmen; Alonso Maleta, Maria Aranzazu
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