Janda, A. (Álvaro)
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- Clogging and unclogging of many-particle systems passing through a bottleneck(EDP Sciences, 2017) Zuriguel-Ballaz, I. (Iker); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel)When a group of discrete particles pass through a narrowing, the flow may become arrested due to the development of structures that span over the size of the aperture. Then, it is said that the system is clogged. Here, we will discuss about the existence of a phase diagram for the clogged state that has been recently proposed, arguing on its usefulness to describe different systems of discrete bodies ranging from granular materials, to colloidal suspensions and live beings. This diagram is built based on the value of a flowing parameter which characterizes the intermittent flow observed in all these discrete systems provided that there is an external or internal energy supply. Such requirement, which is necessary to destabilize the clogging arches, is absent in a standard static silo, which is therefore examined as a particular case. This view will help to understand some a priori inconsistencies concerning the role of driving force in the clogging process that have been found in the last years.
- Fluctuations of grains inside a discharging two-dimensional silo(American Physical Society, 2011-09-26) Zuriguel-Ballaz, I. (Iker); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel)We present experimental data corresponding to a two-dimensional dense granular flow, namely, the gravitydriven discharge of grains from a small opening in a silo. We study the local velocity field at the scale of single grains at different places with the help of particle-tracking techniques. From these data, the velocity profiles can be obtained and the validity of some long-standing approaches can be assessed. Moreover, the fluctuations of the velocities are taken into consideration to characterize the features of the advective motion (due to the gravity force) and the diffusive motion, which shows nontrivial behavior.
- Clogging transition of many-particle systems flowing through bottlenecks(2014) Clement, E. (E.); Pugnaloni, L.A. (Luis A.); Parisi, D.R. (D. R.); Pagonabarraga, I. (Ignacio); Zuriguel-Ballaz, I. (Iker); Peralta, J.P. (Juan Pablo); Cruz-Hidalgo, R. (Raúl); Ferrer, L.M. (Luis Miguel); Lozano, C. (Celia); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel); Gago, P.A. (Paula A.)
- Silo clogging reduction by placing an obstacle above the outlet(AIP Publishing, 2013) Zuriguel-Ballaz, I. (Iker); Lozano, C. (Celia); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel)We present an experimental study of the effect that an obstacle above the outlet of a silo has on the clogging probability. Both, the size of the ori ce and the obstacle position are varied for a chosen obstacle size and shape. If the position of the obstacle is properly selected the clogging probability can be importantly reduced. Indeed, as the outlet size is increased – and we approach the critical size above which there is not clogging – the obstacle effect is enhanced. For the largest outlet size studied, the clogging probability is reduced by a factor of more than one hundred. We will show, using numerical simulations, that the physical parameter behind the reduction of the silo clogging seems to be the decrease of the vertical pressure at the outlet proximities.
- Unjamming a granular hopper by vibration(European Physical Society, 2009-07) Clement, E. (E.); Lanuza, J. (J.); Kolb, E. (E.); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel)We present an experimental study of the outflow of a hopper continuously vibrated by a piezoelectric device. Outpouring of grains can be achieved for apertures much below the usual jamming limit observed for non-vibrated hoppers. Granular flow persists down to the physical limit of one grain diameter, a limit reached for a finite vibration amplitude. For the smaller orifices, we observe an intermittent regime characterized by alternated periods of flow and blockage. Vibrations do not significantly modify the flow rates both in the continuous and the intermittent regime. The analysis of the statistical features of the flowing regime shows that the flow time significantly increases with the vibration amplitude. However, at low vibration amplitude and small orifice sizes, the jamming time distribution displays an anomalous statistics.
- Optimal dynamic control approach in a multi-objective therapeutic scenario: Application to drug delivery in the treatment of prostate cancer(2018) Ardanza-Trevijano, S. (Sergio); Fernández-de-Trocóniz, J.I. (José Ignacio); Janda, A. (Álvaro); Irurzun-Arana, I. (Itziar)Abstract Numerous problems encountered in computational biology can be formulated as optimization problems. In this context, optimization of drug release characteristics or dosing schedules for anticancer agents has become a prominent area not only for the development of new drugs, but also for established drugs. However, in complex systems, optimization of drug exposure is not a trivial task and cannot be efficiently addressed through trial-error simulation exercises. Finding a solution to those problems is a challenging task which requires more advanced strategies like optimal control theory. In this work, we perform an optimal control analysis on a previously developed computational model for the testosterone effects of triptorelin in prostate cancer patients with the goal of finding optimal drug-release characteristics. We demonstrate how numerical control optimization of non-linear models can be used to find better therapeutic approaches in order to improve the final outcome of the patients. Author summary Mathematical models of the disease processes are widely used in computational biology to quantitatively describe the time course of disease progression and are often linked to pharmacokinetic–pharmacodynamic models in order to evaluate the effect of drug treatment on disease. Once the models are built from observed information and/or literature data, they can predict the dynamics of the system under different conditions through computer simulations. However, simulation exercises are not always effective to obtain the desired objectives due to the complexity of these systems. In this work, we optimized the release characteristics of a synthetic gonadotropin-releasing hormone analog used to induce chemical castration by inhibiting the testosterone levels in prostate cancer patients. The therapeutic goals to achieve were to minimize the initial flare up of testosterone levels and the time to reach testosterone values below castration limit, while maximizing the castration period of the patients. Our methodology, based on control theory, introduces a manipulable variable into the system’s equations to drive the model towards the established goals. We demonstrated how drug-release properties can be improved with the implementation of optimal control strategies to enhance the outcome of cancer patients. These methods are extrapolable to other problems encountered in the field.
- Granular flow through an orifice: solving the free fall arch paradox(International Center for Numerical Methods in Engineering, 2015) Zuriguel-Ballaz, I. (Iker); Cruz-Hidalgo, R. (Raúl); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Rubio-Largo, S.M. (Sara María)Several theoretical predictions of the mass flow rate of granular flows through outlets are based on the existence of a free fall arch region covering the silo outlet. Early in the nineteenth century, it was suggested that the particles crossing this region lose their kinetic energy and start to fall freely under their own weight. However, there is not conclusive evidence of this hypothetical region. We examined experimentally and numerically the micro-mechanical details of the particle flow through an orifice placed at the bottom of a silo. Remarkably, the contact stress monotonously decreases when the particles approach to the exit and it only vanishes just at the outlet. The behavior of this magnitude was practically independent of the size of orifice indicating that particle deformation, is insensible to the size of the aperture. Contrary, the behavior of the kinetic stress puts on evidence that the outlet size controls the propagation of the velocity fluctuations inside the silo. Examining this magnitude, we conclusively argue that indeed there is a well-defined transition region where the particle flow changes its nature. Above this region, the particle motion is completely correlated with the macroscopic flow. Our outcomes clarifies why the free fall arch picture has served as an approximation to describe the flow rate in the discharge of silos.
- Flow-rate fluctuations in the outpouring of grains from a two-dimensional silo(The American Physical Society, 2009) Zuriguel-Ballaz, I. (Iker); Cixous, P. (P.); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel); Harich, R. (R.)We present experimental results obtained with a two-dimensional silo discharging under gravity through an orifice at the flat bottom. High-speed measurements provide enough time resolution to detect every single bead that goes out and this allows the measurement of the flow rate in short-time windows. Two different regimes are clearly distinguished: one for large orifices, which can be described by Gaussian fluctuations, and another for small orifices, in which extreme events appear. The frontier between those two regimes coincides with the outlet size below which jamming events are frequent. Moreover, it is shown that the power spectrum of the flow-rate oscillations is not dominated by any particular frequency.
- Silo Clogging Reduction by the Presence of an Obstacle(American Physical Society, 2011-12-29) Zuriguel-Ballaz, I. (Iker); Lozano, C. (Celia); Arevalo, R. (Roberto); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Montero, Á. (Ángel)We present experimental results on the effect that inserting an obstacle just above the outlet of a silo has on the clogging process. We find that, if the obstacle position is properly selected, the probability that the granular flow is arrested can be reduced by a factor of 100. This dramatic effect occurs without any remarkable modification of the flow rate or the packing fraction above the outlet, which are discarded as the cause of the change in the clogging probability. Hence, inspired by previous results of pedestrian crowd dynamics, we propose that the physical mechanism behind the clogging reduction is a pressure decrease in the region of arch formation.
- Disentangling the free-fall arch paradox in silo discharge(2015) Zuriguel-Ballaz, I. (Iker); Cruz-Hidalgo, R. (Raúl); Maza-Ozcoidi, D. (Diego); Janda, A. (Álvaro); Rubio-Largo, S.M. (Sara María)Several theoretical predictions of the mass flow rate of granular media discharged from a silo are based on the spontaneous development of a free-fall arch region, the existence of which is still controversial. In this Letter, we study experimentally and numerically the particle flow through an orifice placed at the bottom of 2D and 3D silos. The implementation of a coarse-grained technique allows a thorough description of all the kinetic and micromechanical properties of the particle flow in the outlet proximities. Though the free-fall arch does not exist as traditionally understood—a region above which particles have negligible velocity and below which particles fall solely under gravity action—we discover that the kinetic pressure displays a well-defined transition in a position that scales with the outlet size. This universal scaling explains why the free-fall arch picture has served as an approximation to describe the flow rate in the discharge of silos.
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