Main

The Workshop

Talks Schedule

Date: 17 to 21 December 2007

Place: Hotel San Martin, Viña del Mar

Participants and Invited Conferences

  • Hector CALISTO, Depto Física, UTA, Chile.
    • Title: "White noisy fluctuations support resonance in nonmultistable systems"
    • Abstract: Stochastic resonance induced by multiplicative white noise in forcing damping nonmultistable oscillator is studied. A stochastic amplitude equation is derived for oscillation envelope, which linearly has stochastic resonance and numerically this phenomenon is persistent when nonlinearities are considered. We describe a simple mechanical system, horizontally driven pendulum, which displays the stochastic resonance.
  • Miguel CALVO, Departamento de Física, Universidad de Valparaíso, Chile.
    • Title: to be announced.
  • Gonzalo CAMEL, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.
  • Marcel CLERC, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.
    • Title: "Interface dynamics of front that connects a stable homogeneous state with a tripe one".
    • Abstract: Interfaces in two-dimensional systems exhibit unexpected complex dynamical behaviors, the dynamics of a border connecting a stripe pattern and a uniform state is studied. Numerical simulations, of a prototype isotropic model, show a zig-zag instability and a complex coarsening process. Close to an spatial bifurcation, the amplitude equation allows us to characterize the coarsening dynamics and the universal behavior exhibited by the model.
  • María L. CORDERO, París, France.
    • Title: "Solutal Marangoni effect in microfluidic droplets".
    • Abstract: Microfluidics is a novel field with multiple potential applications in biology and chemistry, thanks to the posibility of using picoliter droplets as microreactors and implementing lab-on-a-chip technologies. The underlying physics on microfluidics may seem simple, due to the small characteristic Reynolds numbers. However, because of the existence of interfaces and the large area to volume ratio in multiphase microfluidics, various interesting phenomena appear. One of them is shown here: inside a microchannel where water drops in oil are produced, a laser beam is focused. The laser heats the water by absorption, and a temperature gradient is created at the interface of the drop. The presence of surfactant in the oil phase determines the generation of a solutal Maragoni flow at the interface, that indirectly leads to a net force on the drop that can stop its movement. This effect has been shown to be useful as an optical tool to actively control droplets inside the microchannels. Measurements of the temperature increase and of the Marangoni flow inside the drops are shown here, the results show characteristic that are favorable to biological applications.
  • Patricio CORDERO, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.
    • Title:   "The transition line for the rise of a Brazil nut"
    • Abstract: Using molecular dynamics we study the behavior of a large particle immersed in bed of smaller ones.  The system is bidimensional, consisting of many rough inelastic hard disks of equal size plus a larger one: the intruder. They all have the same mass density, hence the intruder is denser than the surrounding "fluid". We keep fixed all possible parameters of the system except for two dimensionless parameters determining the frequency and amplitude of the vibrating base. A systematic exploration of this parameter space leads to determining a transition line separating a zone in which the Brazil nut effect takes place and one in which it does not. The results strongly suggest that there is a minimum amplitude and a maximum frequency for the Brazil nut effect to take place
  • Saliya COULIBALY, Santiago, Chile.
    • Title:   to be announced.
  • Pierre COULLET, Institut Robert Hooke, Université de Nice-Sophia Antipolis, France.
    • Title: to be announced.
  • Roberto DEZA, Mar de Plata, Argentina
    • Title:   to be announced.
  • Jacques DUMAIS, Department of Organismic and Evolutionary Biology, Harvard University, USA.
    • Title: “Cell Morphogenesis - What We Have Learned from Rubber Balloons and Soap Bubbles”.
    • Abstract: Cells acquire a wide range of forms and sizes, often reflecting the intricate functions they serve. Although cells are complex, their geometry is often dictated by well-known physical laws. The idea that simple physical models can shed light on fundamental cell biology problems can be traced back to D.Arcy W. Thompson.s masterpiece “On Growth and Form”. In this seminar, I will present a few examples of the role of mechanics in determining the shape of plant cells.
  • Jocelyn DUNSTAN, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, .Santiago, Chile
  • Gustavo DURING, París, France.
    • Title: "Symmetry effects in capillary wave turbulence".
    • Abstract: We report theoretical and experimental results on 4-wave capillary wave turbulence. We show that a system consisting of two inmiscible and incompressible fluids can be written in a Hamiltonian way. Under some symmetry conditions, the system is simplified and in the small angle aproximation, the set of weakly non-linear interacting waves display a Kolmogorov-Zakharov (KZ) spectrum for the wave amplitud $f^{-8/3}$ in frequency domain or $k^{-4}$ in wave vector space. The system was studied experimentally in a cylindrical cell filled with two inmiscible fluids of almost equal densities (water and silicon oil) where the capillary surface waves are excited by a low frequency random forcing. The power spectral density (PSD) and probability density function (PDF) of the wave amplitudes are studied. Both theoretical and experimental results are in fairly good agreement with each other.
  • Pablo ENCINA, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile
  • Daniel ESCAFF, Universidad de Los Andes, Santiago, Chile
    • Title: "Localized hexagonal patterns: Morphological and size aspects".
    • Abstract: Using a prototype Swift-Hohenberg equation for the order parameter we study the localization mechanism for hexagonal patterns surrounded by a uniform phase. We compare the situation where the hexagonal pattern is localized with the ideal infinite flat front of hexagons under pinning. Numerical simulations show that the existence range for localized structures depends on the size and morphology of the structure. We propose a scale expansion in order to estimate the stress at the interfaces between the hexagons and the uniform phase.
  • Claudio FALCON, París, France.
    • Title: "Fluctuations in out-of-equilibrium systems"
    • Abstract: Nonequilibrium steady state, is usually a fluctuating quantity. There is not yet a universal description of such fluctuations. Here, we show that very different physical systems driven by a random forcing  present identical features for the fluctuations of their injected power. Other related quantities like the heat flux in turbulent convection exhibit the same fluctuations. Then we will detailled the derivation of an exact analytical formula of the PDF of these fluctuations in the simplest case of this class of dissipative system. The agrements and discrepancies of these PDF with the ones obtained in other dissipative systems are discussed.  Further extensions of these works, espacially for energy flux in turbulent flows will be discussed to conclude.
  • Andrés GOMBEROFF, Universidad Andrés Bello.
    • Title:   "Topics in Gravitational phase transitions and black hole thermodynamics".
  • Pablo GUTIERREZ, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile
  • Eugenio HAMM, Santiago, Chile.
    • Title: “Tearing and peeling of elastic surfaces”.
    • Abstract: We study the propagation of fragile fracture in a thin elastic surface with simultaneous peeling-off from a solid substrate when external forcing involves large displacements out of the reference plane. We consider the case of two initially parallel cracks separated by a flap of material. By bending and pulling the flap at constant velocity, cracks immediately start to propagate towards one another, finally merging at a point. The remanent strip has a triangular shape whose characteristic angle results from the interplay between work of fracture / bending stiffness of the elastic surface and adhesion energy. Our result constitutes a test that may give valuable information on mechanical properties of the material and its adhesion to the substrate.
  • Giorgio KRSTULOVIC, Laboratoire de Physique Statistique, Ecole Normale Supérieure, Paris, France.
    • Title: “Two-fluid model for the truncated Euler equations”.
    • Abstract: A phenomenological two-fluid model of the (time-reversible) spectrally-truncated 3D Euler equation is proposed. The thermalized small scales are first  shown to be quasi-normal. The effective viscosity and thermal diffusion are then determined, using EDQNM closure and Monte-Carlo numerical computations. Finally, the model is validated by comparing its dynamics with that of the original truncated Euler equation.
  • David LAROZE, Santiago, Chile.
    • Title:   to be announced.
  • Fernando LUND, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile
    • Title: "Ultrasound as a Probe of Plasticity".
  • Javier MARTINEZ, Valparaíso, Chile
  • Alejandra MONTECINOS, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile
  • Michel MOREAU, Laboratory of Theoretical Physics of Condensed Matter, Université Pierre et Marie Curie, Paris, France.
    • Title: “Intermittent search processes and reaction kinetics in heterogeneous media.
    • Abstract: Intermittent search processes alternate two different stochastic motions in order to reach a given target. If the faster motion has a lower probability to detect the target, a contest is possible concerning the efficiency of both processes, and it may be possible to minimize the search time by a convenient choice of the alternation. This argument has been used to interpret observations in molecular biology or to explain the behaviour of animals searching for food. Here we show that it can have interesting consequences for the kinetics of reactions in heterogeneous media. First, we assume that the reaction can only be completed at an interface, whereas the active molecules temporarily pass into another phase, where it is dragged by a flow, before returning to the reactive interface. A second case concerns reaction kinetics in a biological cell, when the active molecules can occasionally bind to molecular motors which inactivate their reactivity but transport them far away. Both cases frequently occurs in actual situations. We show that the overall reactivity can be significantly enhanced by such an intermittent behaviour.
  • Nicolás MUJICA, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile
    • Title: "Liquid-solid-like transition in quasi-one-dimensional driven granular media".
    • Abstract: The theory of non-ideal gases in thermodynamic equilibrium, for instance the van der Waals gas model, has played a central role in the understanding of coexisting phases as well as in the transition between them. Granular matter contrasts with these gases because the collisions between grains dissipate energy, and their macroscopic size renders thermal fluctuations negligible. If a mass of grains is subjected to mechanical vibration, it can make a transition to a fluid state. In this state, granular matter exhibits patterns and instabilities that resemble those of molecular fluids. Here, we report a granular solid-liquid phase transition in a vibrating granular monolayer. The transition is mediated by waves and is triggered by a negative compressibility as in van der Waals phase coexistence, although the system  does not satisfy the hypotheses used to understand atomic systems. The dynamic behaviour that we observe---coalescence, coagulation, wave propagation---is common to a wide class of phase transitions. We have combined experimental, numerical and theoretical studies to understand the different features of this transition.
  • Carlos ORELLANA, Chicago, USA
    • Title: "Dynamics of a thin granular layer with periodic flow modulation".
    • Abstract: We present an experimental study of the dynamics of a quiasi one dimentional thin granular layer with periodic flow modulation, with special emphasis in the dynamical transition on the layer and the effects of noise on them.
  • Loreto OYARTE, Santiago, Chile
  • Darío PEREZ, Valparaíso, Chile
    • Title:   to be announced.
  • Luca POCIVAVSEK, Department of Chemistry and JFI, University of Chicago, Chicago IL, 60637 USA.
    • Title:  “Wrinkling to Folding Transition in Thin Elastic Sheets”.
    • Abstract: Crumple an elastic sheet and it forms a patched pattern of flat regions separated by highly deformed ridges. Now compress a similar membrane resting on some substrate and the response is different. First wrinkles form where the bending stresses are distributed throughout the surface. However compressing further (in particular by a third of the initial wavelength) leads to stress focusing at particular points on the surface. Yet the folds which develop are different from the well understood ridges in unsupported sheets. We explore the transition from wrinkles to folds and show how such a transition can explain a long-standing problem in lipid monolayers.
  • Araceli PROTO, Buenos Aires, Argentina
    • Title:   "Gibbs entropy and nonlinear semiquantum dynamics"
    • Abstract: We describe here how by departing from the Gibbs entropy [1-3] it is possible to deal with semiquantum time-independent, nonlinear Hamiltonians. The entanglement between the quantal and classical degrees of freedom can be easily seen, and the set of differential equations that governs the temporal evolution of the quantal mean values and the classical variables is obtained. Thermodynamical aspects can be also described. We found invariants of motion, and particularly we described under which contitions the Uncertainty Principle is also an invariant of motion. Through the analysis of these invariants, it is possible to conclude that semiquantum systems "never forgets" its quantum nature. A simple example is shown.
  • Sebastián REYES, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile
  • Sergio RICA, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.
  • Benoit ROMAN, Laboratoire de Physique et Mécanique des Milieux Hétérogènes, École Supérieure de Physique et de Chimie Industrielles (ESPCI), Paris, France.
    • Title:   “Elasticity and capillarity : wet hairs and origami”.
    • Abstract: Capillary forces are responsible for a large range of everyday observations : the shape of rain droplets, the imbibition of a sponge, the clumping of wet hair into bundles. Although they are often negligible on macroscopic structures, surface capillary forces may overcome volume forces at small scales and deform compliant micro-structures. Capillary-induced sticking can indeed prevent the actuation of mobile elements in micro-electro- mechanical systems (MEMS), or even cause their collapse. Capillary forces also have important consequences in biology such as the buckling of the airway lumen induced by surface tension, which can eventually cause the lethal closure of lung airways (known as neonatal respiratory distress syndrome). We will review a few experimental situations where capillary forces are able to deform two types of objects: rods, and thin sheets. For instance, wet hairs tend to assemble into bundles through a cascade of successive pairings. Comparing attracting capillary forces to bending elasticity, leads to a characteristic "elasto-capillary" length. The case of thin sheets is challenging because of geometrical constrains, which generally leads to singularities. Can a thin sheet spontaneously wrap around droplet? We will describe in detail this "capillary origami" experiment.
  • René ROJAS, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.
    • Title: to be announced.
  • Francisco SANTIBAÑEZ, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.
    • Title: "Nonlinear waves in dry and wet Hertzian granular chains".
    • Abstract: A report on previous and recent results of experiments and numerical analysis for the propagation of nonlinear waves in one.dimensional Hertzian chains will be presented. The introduction of heterogeneities (e.g. local modification of the inertia and stiffness), in a Hertzian chain, produces new interesting phenomena which are studied by means of in.situ force measurements and numerical simulations. We consider first, a monodisperse chain as a reference case, then we study the modifications of the nonlinear pulse in different chain configurations. Finally, in this talk, I will present some recent experimental results concerning the effect of introducing a thin layer of fluid between contacts. Work with Stephane Job and Francisco Melo.
  • Guillermo SAVINO, San Miguel de Tucumán, Argentina.
    • Title: "Nonlinear analog electronic intrinsic burster as a novel bursting neuron model".
    • Abstract: The design of electronic nonlinear devices modeling complex oscillations is often difficult due to both: the lack of general constructive rules, and stability problems related with the dynamical robustness of the circuits. Usually a parameter's fine tuning becomes unavoidable. Here we describe a simple dynamically robust nonlinear analog electronic circuit with intrinsic stable bursting and spiking oscillations. Although, the circuit does not reproduce faithfully the neuron's action potential waveform, it can be considered a bursting neuron model, because it is change-conduction-based, and shows the same bifurcations scenario preserving dynamics of the classical Hodgkin-Huxley equations. The circuit is based on the nontrivial nonlinear interaction of a fast currents "voltage dependant" circuit block and a slow currents "time dependant" circuit block. It allows a qualitatively explanation of bursting and spiking generation and to pose some interesting questions to be tested in real neurons. Also the burster properties to external noise are shown. Work with Carlos M. Formigli.
  • Rodrigo SOTO, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.
    • Title: to be announced.
  • Raúl TORAL, Instituto de Fisica Interdisciplinar y Sistemas Complejos (IFISC), CSIC-UIB, Campus Universitat Illes Balears, E-07122 PalmaS de Mallorca, Spain.
    • Title:    “Constructive role of diversity in the synchronization of dynamical systems”.
  • Simón VILLAIN-GUILLOT, Bordeaux, France
    • Title: to be announced.
  • Francisco VIVANCO, Santiago, Chile
    • Title: "Underground mining flows: an application of Kinematic and Plasticity models".
    • Abstract: The Kinematic and Plasticity models have been proved to be succesful in the description of granular flows in flat bottomed hoppers and in systems with radial flow respectively. Recently, these models have been applied to the description of rocks flow when the block caving technique is applied to the underground mining process. Here we introduce both models and used it to determine the isolated movement and extracted zones observed in the laboratory scale experiments. The dilation effects introduced as a local density change is considered in order to determine the isolated movement zone. The results obtained are compared with ratio of isolated movement to extracted heights proposed by Janelid and Kvapil[2] H_imz/H_iez~2.5, showing that a density change of 25% in two dimensions and 16% in three dimensions are required to fulfill the Janelid and Kvapil relation. Also, the predicted isolated movement and extracted zones are compared to Castro et[3] experimental data obtaining a good agreement with the behavior observed in their curves for the height and width as a function of the extracted volume and the width as a function of height on both zones. The rock size effect in the maximum width of isolated extracted zone is also calculated showing that both Peters[4] and Power[5] data are compatible with the kinematic model predictions.

      [1] Melo F, Vivanco F, Fuentes C and Apablaza V. Kinematic model for quasi static granular displacements in block caving: Dilatancy effect on drawbody shapes, Int J Rock Mech Min Sci (2007), DOI:10.1016/j.ijrmms.2007.07.005.
      [2] Janelid I. and Kvapil R. Sublevel caving, Int J Rock Mech Min Sci, 1966;3:129-153.
      [3] Castro R., Trueman R., Halim A. A study of isolated draw zones in block caving mines by means of a large 3D physical model, Int J Rock Mech Min Sci, 2007;44:860-870.
      [4] Peters D.C. Physical modeling of the draw behavior of broken rock caving, Quarterly of the Colorado School of Mines, 1984;79.
      [5] Power G.R. Modeling granular flow in caving mines: large scale physical modeling and full scale experiments. PhD thesis, The University of Queensland, Brisbane, 2004.
  • Jaime ZUÑIGA, Departamento de Física, Fac. Cs. Físicas y Matemáticas, Univ. De Chile, Santiago, Chile.