L. G. Sarasua

Universidad de la República de Uruguay | UdelaR

In this work, on the one hand, we continue with the study of the dynamic property of Beltrami flows [R. González, “Dynamics of non-axisymmetric Beltrami flows,” Phys. Fluids 26, 114104 (2014)], extending its scopes to non-stationary flows in the rotating system, which allowed us to classify the rotating waves on the basis of their phase velocities....

In this work several lagrangian methods were used to analyze the mixing and transport processes in an experimental model of a constricted artery under a pulsatile flow. Upstream Reynolds number $Re$ was changed between 1187 and 1999, while the pulsatile period $T$ was kept fixed at 0.96s. Velocity fields were acquired using Digital Particle Image V...

We analyse the flow organization of turbulent fountains in stratified media under different conditions, using three-dimensional finite-time Lyapunov exponents. The dominant Lagrangian coherent structures responsible for the transport barriers in three different configurations suggest a self-similarity behaviour. After proposing a criterion for deli...

We study the development and decay of vortex in viscoelastic fluids between coaxial cylinders by means of experiments with solutions of polyacrylamide and glycerin and numerical simulations. The transient process is triggered when the inner cylinder is either abruptly started or stopped while the outer is kept fixed. The azimuthal velocity, obtaine...

We study the development and decay of vortex in viscoelastic fluids between coaxial cylinders by means of experiments with solutions of polyacrylamide and glycerin and numerical simulations. The transient process is triggered when the inner cylinder is either abruptly started or stopped while the outer is kept fixed. The azimuthal velocity, obtaine...

This work presents a study based on numerical simulations to describe the local structural evolution of Cu-Zr-Al amorphous alloys when moderate stresses are applied and removed. In particular, it will seek to recognize the formation of clusters with some degree of symmetry in the amorphous matrix and how these are altered depending on the mechanica...

This study analyzed the influence of low-temperature elastic ultrasonic stimulus on the local structural order of Cu47.5Zr45.5Al5Er2 amorphous alloy, using the ultrasonic pulse-echo technique with a longitudinal wave frequency of 10 MHz, between 100 K to 300 K under consecutive cryogenic thermal cycles. Ultrasonic attenuation and wave velocity data...

Axisymmetric fountains in stratified environments rise until reaching a maximum height, where the vertical momentum vanishes, and then fall and spread radially as an annular plume following a well-known top-hat profile. Here, we generalize the model of Morton et al. [“Turbulent gravitational convection from maintained and instantaneous sources,” Pr...

Axisymmetric fountains in stratified environments rise until reaching a maximum height, where the vertical momentum vanishes, and then falls and spread radially as an annular plume following a well-known top-hat profile. Here, firstly, we generalize the model of Morton et al. (Proc. R. Soc. Lond. A \textbf{234}, 1, 1956), in order to correctly dete...

Improved understanding of how vortices develop and propagate under pulsatile flow can shed important light on the mixing and transport processes occurring in such systems, including the transition to turbulent regime. For example, the characterization of pulsatile flows in obstructed artery models serves to encourage research into flow-induced phen...

An improved understanding of how vortices develop and propagate under pulsatile flow can shed important light on the mixing and transport processes including the transition to turbulent regime occurring in such systems. For example, the characterization of pulsatile flows in obstructed artery models serves to encourage research into flow-induced ph...

We experimentally study the time evolution of the distance between two identical spheres settling down in polyacrylamide shear-thinning solutions in mixtures of water and glycerin. In order to analyze the behavior of the spheres under different rheological conditions, we varied the concentration of the polymer and glycerin. To examine the influence...

In this work, we study the average time a Brownian oscillator coupled to a thermal bath takes to get fluctuations of a given energy. The waiting times are obtained as a function of the system parameters using the Langevin equation and molecular simulations. We found that an oscillators system can exhibit arbitrarily large transient violations of th...

We present a demonstration of the equivalence between the Kelvin-Planck statement of the second law and the principle of entropy increase. Despite the fundamental importance of these two statements, a rigorous treatment to establish their equivalence is missing in standard physics textbooks. The argument is valid under very general conditions, but...

Abstract An experimental investigation into the interaction between a turbulent fountain and its stratified environment is presented. A heavy fluid, cold water, is injected vertically upwards into a linearly stratified medium. As revealed by visualisations, the heavy-fluid jet reaches a maximum height before it begins to fall under to the effect of...

The dependence with temperature of elastic modulus of relaxor ferroelectric ceramics is modeled with a Landau-Devonshire-type cluster theory. The effective elastic modulus obtained from experimental data of ultrasonic longitudinal velocity in PCT and PLZT ferroelectric ceramics are compared with the proposed model. This comparison shows that the mo...

A laboratory simulation was assessed for its capacity to reproduce the actual conditions found in a microburst. In our experimental set-up, the flow was driven by combined impinging jet and density perturbations forcing with the aim of determining their relative influence on the overall microburst behavior and, in particular, the initiation and str...

In this work we study the scour produced by a jet downstream of a submerged sluice gate on a sediment bed of non-cohesive particles. The experiments were performed for various values of sill heights and {\deg}uid depths. New regimes were observed in which two holes are simultaneously developed. We identify the origins of the two holes and show that...

In the present work we consider the relation between superconductivity and spontaneous gauge symmetry breaking (SGBS). We show that ODLRO does not require in principle SBGS, even in the presence of particle number fluctuations, by examining exact solutions of a fermionic pairing model. The criteria become equivalent if a symmetry breaking field is...

The axisymmetric flow inside a cylindrical container with a rod along its symmetry axis is studied. The flow is produced by the rotation of one of the cylinder end walls, of both end walls, or of the sidewall. Analytical expressions (for low Reynolds numbers) of the azimuthal velocity field are presented, thus extending the solutions of the case wi...

We obtain exact ground states of an extended periodic Anderson model (EPAM) with non-local hybridization and Coulomb repulsion between f and c electrons (Falicov–Kimball term) in one dimension. We show that for a range of parameter values these ground states exhibit composite hole pairing and superconductivity that originate from purely electronic...

In this work, we study superconductivity in the strong coupling limit of the two-dimensional Hubbard model using a generalization of the Hubbard-I approximation. The results are compared with those obtained by Beenen and Edwards with the two-pole method of Roth, revealing a qualitative agreement between the two approaches. The effect of the hopping...

The papers published in this volume of the Journal of Physics: Conference Series were selected from the manuscripts submitted to the XI Meeting on Recent Advances in the Physics of Fluids and their Applications (FLUIDOS2010), which was held in Colonia del Sacramento, Uruguay, 3–5 November 2010. FLUIDOS takes place every two years, usually in Novemb...

The effect of polymer concentration on the development of reverse secondary flow and vortex breakdown was studied using a viscoelastic solution of polyacrlylamide in water. The fluid was contained in cylindrical containers of two different radii, the top end wall of which rotated at a varying speed, thus, imparting a circulating motion to the fluid...

The interaction between a turbulent fountain and its stratified environment was studied. A heavy fluid, cold water, was injected vertically upwards into a linearly stratified medium. The round heavy-fluid jet reaches a maximum height before it begins to fall due to the effect of gravity. Because of the effects of friction and mixing, the vertical m...

The effect of stationary cylindrical rods located at the centerline axis on the vortex breakdown (VB) in a closed flow is studied experimentally and numerically. The flow takes place in a cylindrical container with a rotating end wall. The dimensionless numbers characterizing the dynamics of the system are the Reynolds number, based on the angular...

Two-layer stratified flows over abrupt topographic obstacles, simulating relevant situations in oceanographic problems, are investigated numerically and experimentally in a simplified two-dimensional situation. Experimental results and numerical simulations are presented at low-to-intermediate Froude numbers for two different obstacles: one semicyl...

In this work we study the double exchange-Holstein model with an electron-phonon interaction γ coupled to magnetism. The analysis is performed combining a mean-field approximation for the double exchange interaction and the Lang-Firsov transformation for the electron-phonon interaction. Discontinuous magnetic transitions appear when the dependence...

The flow of a two--layer stratified fluid over an abrupt topographic obstacle, simulating relevant situations in oceanographic problems, is investigated numerically and experimentally in a simplified two--dimensional situation. Experimental results and numerical simulations are presented at low Froude numbers in a two-layer stratified flow and for...

The effect of fixed cylindrical rods located at the centerline axis on vortex breakdown (VB) is studied experimentally and numerically. We find that the VB is enhanced for very small values of the rod radius $d$, while it is suppressed for values of $d$ beyond a critical value. In order to characterize this effect, the critical Reynolds number for...

In this work we show that when an inviscid axisymmetric Rankine flow experiences a soft expansion, rotating Kelvin waves can be excited. Downstream of the region where the expansion occurs (the transition region) the resulting flow can be expressed as the addition of a Rankine and a Beltrami flow. The Beltrami constant is determined from the Rankin...

In the present work we study numerical and experimentally the flow of a two-layer stratified fluid over a topographic obstacle. The problem reflects a wide number of oceanographic and meteorological situations, where the stratification plays an important role. We identify the different instabilities developed by studying the pycnocline deformation...

In this work, we study an extended version of the t-J model. For special values of the hopping parameters we obtain exactly the ground state of the model. We found that depending on the values of the system parameters, the ground state may be superconducting, a charge ordered insulator, or a phase separated state. As holes are added to the system,...

This work is focused to study the development and control of the laminar vortex breakdown of a flow enclosed in a cylinder. We show that vortex breakdown can be controlled by the introduction of a small fixed rod in the axis of the cylinder. Our method to control the onset of vortex breakdown is simpler than those previously proposed, since it does...

We study the formation of helical vortex filaments in a tube. The helical flow is assumed to be potential except in a very slender core. The boundary conditions are satisfied by introducing a helical image vortex. By assuming an axisymmetric flow upstream and imposing conservation laws, we obtain a set of conditions that must be satisfied by the he...

In this work we study superconductivity in the periodic Anderson model with both on-site and intersite hybridization, including the interband Coulomb repulsion. We show that the presence of the intersite hybridization together with the on-site hybridization significantly affects the superconducting properties of the system. The symmetry of the hybr...

We study the interplay between superconductivity and excitonic correlations in a two-band model, in the presence of hybridization and local repulsion between electrons of different bands. The ground-state phase diagram as a function of the hybridization V and the interband Coulomb repulsion G is constructed. There is a critical value of hybridizati...

Using information theory, a new variational principle for incompressible fluids is derived. This principle is similar to a known plasma stability criterion which has successfully been applied to study the stability of different steady flows. Its main advantages, when compared to traditional methods, are: (1) to obtain the stability of a given equil...

The effect of the viscosity on the linear stability of a swirling top hat jet with nonrotating core is studied analytically. Numerical values of the growth rate are obtained. It is shown that the viscosity induces instabilities in the region of wave numbers where no inviscid instability occurs. In the short wave limit, the asymptotic solution revea...