Facultad de Ciencias
Permanent URI for this communityhttps://hdl.handle.net/10171/113
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309 results
Results
- Granular internal dynamics in a silo discharged with a conveyor belt(Cambridge University Press, 2021) Zuriguel-Ballaz, I. (Iker); Maza-Ozcoidi, D. (Diego); Gella, D. (Diego)The dynamics of granular media within a silo in which the grain velocities are controlled by a conveyor belt has been experimentally investigated. To this end, the building of coarse-grained field maps of different magnitudes has allowed a deep analysis of the flow properties as a function of two parameters: the orifice size and the belt velocity. First, the internal dynamics of the particles within the silo has been fully characterized by the solid fraction, the velocity of the particles and the kinetic stress. Then, the analysis of the vertical profiles of the same magnitude (plus the acceleration) has allowed connection of the internal dynamics with the flow rate. In particular, we show that the gamma parameter – which accounts for the integration of the normalized acceleration along the vertical direction – can successfully discriminate the kind of flow established within the silo (from the quasistatic regime to the free discharge) depending on the outlet size and belt velocity.
- Aggregation of T -subgroups(Elsevier, 2023) Natividade, M. (M.) de; Ardanza-Trevijano, S. (Sergio); Talavera, F.J. (Francisco Javier); Elorza-Barbajero, J. (Jorge); Chasco, M.J. (María Jesús)We study when an aggregation function acting on an n-tuple of T-subgroups preserves the structure of T-subgroup. First we need to consider that there are two known definitions applicable to the aggregation of structures on fuzzy sets. These two notions differ in the domain of the aggregated structure. It is known that for indistinguishability operators, pseudometrics, quasi-pseudometrics among others, the aggregation functions that preserve these structures are the same with both definitions. However this is not the case for quasi-metrics. In this line we study the aggregation of T-subgroups with both definitions and their implications. We see that aggregation functions may preserve the structure of T-subgroups with one definition but not with the other. However, under adequate restrictions, the aggregation functions preserving the structure of T-subgroups are the same with either definition. We also show that the results depend on the structure of the subgroup lattice of the ambient group, the particular T-subgroups being aggregated, or the aggregation function.
- Aggregation of fuzzy graphs(Elsevier, 2024) Bejines-López, C. (Carlos); Ardanza-Trevijano, S. (Sergio); Talavera, F.J. (Francisco Javier); Elorza-Barbajero, J. (Jorge)Our study is centered on the aggregation of fuzzy graphs, looking for conditions under which the aggregation process yields another fuzzy graph. We conduct an in-depth analysis of the preservation of several important properties and structures inherent to fuzzy graphs, like paths, cycles, or bridges. In addition we obtain appropriate criteria for when the aggregation of complete fuzzy graphs is again a complete fuzzy graph.
- Aggregation of T-subgroups of groups whose subgroup lattice is a chain(Elsevier, 2023) Ardanza-Trevijano, S. (Sergio); Elorza, J. (Jennifer); Talavera, F.J. (Francisco Javier); Bragard, J. (Jean)In this work, we study when an aggregation operator preserves the structure of T-subgroup of groups whose subgroup lattice is a chain. There are two widely used ways of defining the aggregation of structures in fuzzy logic, previously named on sets and on products. We will focus our attention on the one called aggregation on products. When the lattice of subgroups is not a chain, it is known that the dominance relation between the aggregation operator and the t-norm is crucial. We show that this property is again important for some of the groups in this study. However, for the rest of them, we must define a new property weaker than domination, that will allow us to characterize those operators which preserve T-subgroups.
- Study of type-III intermittency in the Landau–Lifshitz-Gilbert equation(IOP, 2021) Laroze, D. (David); Pérez, L.M. (L. M.); Barrientos, R.J. (R. J.); Bragard, J. (Jean); Riquelme, J.A. (J. A.); Hernández-García, R. (R.); Vélez, J.A. (J.A.)We have studied a route of chaos in the dissipative Landau–Lifshitz-Gilbert equation representing the magnetization dynamics of an anisotropic nanoparticle subjected to a time-variant magnetic field. This equation presents interesting chaotic dynamics. In the parameter space, for some forcing frequency and magnetic strength of the applied field, one observes a transition from a regular periodic behavior to chaotic dynamics. The chaotic dynamics, close to the bifurcation, are characterized by type-III intermittency. Long epochs of quasi-regular dynamics followed by turbulent bursts. The characterization of the intermittencies has been done through four different techniques. The first method is associated with the computation of the Lyapunov exponents that characterize the chaotic regime. The second and third methods are associated with the statistics of the duration of the laminar epochs prior to a turbulent burst. The fourth method is associated with the subharmonic instability present in those laminar epochs and quantified through a Poincaré section method. At the end of the manuscript, we compare the result obtained by the different techniques and discuss the methods' limitations.
- Mechanistic characterization of oscillatory patterns in unperturbed tumor growth dynamics: The interplay between cancer cells and components of tumor microenvironment(PLOS, 2023) Mangas-Sanjuan, V. (Víctor); Parra-Guillen, Z.P. (Zinnia Patricia); Troconiz, I.F. (Iñaki F.); Sancho-Araiz, A. (Aymara); Ardanza-Trevijano, S. (Sergio); Bragard, J. (Jean)Mathematical modeling of unperturbed and perturbed tumor growth dynamics (TGD) in preclinical experiments provides an opportunity to establish translational frameworks. The most commonly used unperturbed tumor growth models (i.e. linear, exponential, Gompertz and Simeoni) describe a monotonic increase and although they capture the mean trend of the data reasonably well, systematic model misspecifications can be identified. This represents an opportunity to investigate possible underlying mechanisms controlling tumor growth dynamics through a mathematical framework. The overall goal of this work is to develop a data-driven semi-mechanistic model describing non-monotonic tumor growth in untreated mice. For this purpose, longitudinal tumor volume profiles from different tumor types and cell lines were pooled together and analyzed using the population approach. After characterizing the oscillatory patterns (oscillator half-periods between 8–11 days) and confirming that they were systematically observed across the different preclinical experiments available (p<10−9), a tumor growth model was built including the interplay between resources (i.e. oxygen or nutrients), angiogenesis and cancer cells. The new structure, in addition to improving the model diagnostic compared to the previously used tumor growth models (i.e. AIC reduction of 71.48 and absence of autocorrelation in the residuals (p>0.05)), allows the evaluation of the different oncologic treatments in a mechanistic way. Drug effects can potentially, be included in relevant processes taking place during tumor growth. In brief, the new model, in addition to describing non-monotonic tumor growth and the interaction between biological factors of the tumor microenvironment, can be used to explore different drug scenarios in monotherapy or combination during preclinical drug development.
- Periodicity characterization of the nonlinear magnetization dynamics(AIP, 2020) Laroze, D. (David); Suárez, O.J. (O. J.); Cabanas, A.M. (A.M.); Pérez, L.M. (L. M.); Bragard, J. (Jean); Mancini-Maza, H. L. (Hector Luis); Vélez, J.A. (J.A.)In this work, we study numerically the periodicity of regular regions embedded in chaotic states for the case of an anisotropic magnetic particle. The particle is in the monodomain regime and subject to an applied magnetic field that depends on time. The dissipative Landau–Lifshitz–Gilbert equation models the particle. To perform the characterization, we compute several two-dimensional phase diagrams in the parameter space for the Lyapunov exponents and the isospikes. We observe multiple transitions among periodic states, revealing complex topological structures in the parameter space typical of dynamic systems. To show the finer details of the regular structures, iterative zooms are performed. In particular, we find islands of synchronization for the magnetization and the driven field and several shrimp structures with different periods.
- Decoupling Geometrical and Kinematic Contributions to the Silo Clogging Process(2018) Zuriguel-Ballaz, I. (Iker); Maza-Ozcoidi, D. (Diego); Gella, D. (Diego)Based on the implementation of a novel silo discharge procedure, we are able to control the grains velocities regardless of the outlet size. This allows isolating the geometrical and kinematic contributions to the clogging process. We find that, for a given outlet size, reducing the grains velocities to extremely low values leads to a clogging probability increment of almost two orders of magnitude, hence revealing the importance of particle kinematics in the silo clogging process. Then, we explore the contribution of both variables, outlet size and grains velocity, and we find that our results agree with an already known exponential expression that relates clogging probability with outlet size. We propose a modification of such expression revealing that only two parameters are necessary to fit all the data: one is related with the geometry of the problem, and the other with the grains kinematics.
- Clogging-jamming connection in narrow vertical pipes(2020) Zuriguel-Ballaz, I. (Iker); López, D. (Diego); Cruz-Hidalgo, R. (Raúl); Maza-Ozcoidi, D. (Diego); Hernández-Delfín, D. (Dariel)We report experimental evidence of clogging due to the spontaneous development of hanging arches when a granular sample composed of spherical particles flows down a narrow vertical pipe. These arches, akin to the ones responsible for silo clogging, can only be possible due to the role of frictional forces; otherwise they will be unstable. We find that, contrary to the silo case, the probability of clogging in vertical narrow tubes does not decrease monotonically with the ratio of the pipe-to-particle diameters. This behavior is related to the clogging prevention caused by the spontaneous ordering of particles apparent in certain aspect ratios. More importantly, by means of numerical simulations, we discover that the interparticle normal force distributions broaden in systems with higher probability of clogging. This feature, which has been proposed before as a distinctive feature of jamming in sheared granular samples, suggests that clogging and jamming are connected in pipe flow.
- Harmonically driven slider: Markovian dynamics between two limiting attractors(2019) Schins, J.M.; Maza-Ozcoidi, D. (Diego)We present experimental data of the motion of a cylindrical slider interacting only by friction with a polished horizontal tray. The tray is harmonically shacked in the horizontal direction. Below a certain threshold of the driver acceleration, the slider permanently sticks to its substrate due to the static friction. Above that threshold, the observed slider dynamics is periodic (synchronous with the driver oscillation frequency) but not wholly harmonic: for driver accelerations little beyond the threshold, the slider velocity signal is quasi-triangular. A Markovian model shows that, with increasing driver acceleration, the slider motion increasingly tends to be harmonic again, though with a prominent phase difference respect to the driver.