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Using a multi-orifice cylindrical silo, the average flow rates Q1 and QN through one and N orifices, respectively, were first measured for the discharge of water or dry grains and then for the mixture. As expected, Q N = N Q 1 for monophasic discharges. Nevertheless, for the mixture, Q N ≪ N Q 1 , and the effect becomes more notorious as N augments and when the grain size is decreased. A simplified continuum model of a flow through a dynamic porous medium, with hydrodynamic resistance that increases with N, is used to reproduce the experimental results. Additional analysis in a two-dimensional cell reveals interacting parabolic flow profiles of the immersed particles close to the orifices, with a reduction in the average velocities when N is increased, which helps to understand the non-additivity of the total flow rate. [ABSTRACT FROM AUTHOR]

In various types of many-particle systems, bidispersity is frequently used to avoid spontaneous ordering in particle configurations. In this study, the relation between bidispersity and disorder degree of particle configurations is investigated. By using magnetic dipole–dipole interaction, magnet particles are dispersed in a two-dimensional cell without any physical contact between them. In this magnetic system, bidispersity is introduced by mixing large and small magnets. Then, the particle system is compressed to produce a uniform particle configuration. The compressed particle configuration is analyzed by using Voronoi tessellation for evaluating the disorder degree, which strongly depends on bidispersity. Specifically, the standard deviation and skewness of the Voronoi cell area distribution are measured. As a result, we find that the peak of standard deviation is observed when the numbers of large and small particles are almost identical. Although the skewness shows a non-monotonic behavior, a zero skewness state (symmetric distribution) can be achieved when the numbers of large and small particles are identical. In this ideally random (disordered) state, the ratio between pentagonal, hexagonal, and heptagonal Voronoi cells becomes roughly identical, while hexagons are dominant under monodisperse (ordered) conditions. The relation between Voronoi cell analysis and the global bond orientational order parameter is also discussed. [ABSTRACT FROM AUTHOR]

We investigate the structural relaxation of a soft-sphere liquid quenched isochorically (ϕ = 0.7) and instantaneously to different temperatures Tf above and below the glass transition. For this, we combine extensive Brownian dynamics simulations and theoretical calculations based on the non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory. The response of the liquid to a quench generally consists of a sub-linear increase of the α-relaxation time with system's age. Approaching the ideal glass-transition temperature from above (Tf > Ta), sub-aging appears as a transient process describing a broad equilibration crossover for quenches to nearly arrested states. This allows us to empirically determine an equilibration timescale teq(Tf) that becomes increasingly longer as Tf approaches Ta. For quenches inside the glass (Tf ≤ Ta), the growth rate of the structural relaxation time becomes progressively larger as Tf decreases and, unlike the equilibration scenario, τα remains evolving within the whole observation time-window. These features are consistently found in theory and simulations with remarkable semi-quantitative agreement and coincide with those revealed in a previous and complementary study [P. Mendoza-Méndez et al., Phys. Rev. 96, 022608 (2017)] that considered a sequence of quenches with fixed final temperature Tf = 0 but increasing ϕ toward the hard-sphere dynamical arrest volume fraction ϕ H S a = 0.582. The NE-SCGLE analysis, however, unveils various fundamental aspects of the glass transition, involving the abrupt passage from the ordinary equilibration scenario to the persistent aging effects that are characteristic of glass-forming liquids. The theory also explains that, within the time window of any experimental observation, this can only be observed as a continuous crossover. [ABSTRACT FROM AUTHOR]

The flow rate of water through an orifice at the bottom of a container depends on the hydrostatic pressure whereas for a dry granular material it is nearly constant. But what happens during the simultaneous discharge of grains and liquid from a silo? By measuring the flow rate as a function of time, we found that (i) different regimes appear, going from the constant flow rate to a hydrostatic-like discharge depending on the aperture size and grain diameter, (ii) the mixed material is always discharged faster than dry grains but slower than liquid, (iii) for the mixture, the liquid level drops faster than the grain level, but they are always linearly proportional to one another, and (iv) a sudden growth in the flow rate happens during the transition from a biphasic discharge to a single phase discharge. These results are associated to the competition between the decrease in hydrostatic pressure above the granular bed and the hydrodynamic resistance. A model combining Darcy’s law with Bernoulli and mass conservation equations is proposed, and the numerical results are in good agreement with experiments. [ABSTRACT FROM AUTHOR]

We illustrate how a simple statistical model can describe the quasiperiodic occurrence of large earthquakes. The model idealizes the loading of elastic energy in a seismic fault by the stochastic filling of a box. The emptying of the box after it is full is analogous to the generation of a large earthquake in which the fault relaxes after having been loaded to its failure threshold. The duration of the filling process is analogous to the seismic cycle, the time interval between two successive large earthquakes in a particular fault. The simplicity of the model enables us to derive the statistical distribution of its seismic cycle. We use this distribution to fit the series of earthquakes with magnitude around six that occurred at the Parkfield segment of the San Andreas fault in California. Using this fit, we estimate the probability of the next large earthquake at Parkfield and devise a simple forecasting strategy. [ABSTRACT FROM AUTHOR]

An analytic expression for the total energy of 4He clusters composed of N atoms is obtained by means of a variational solution of the energy density functional. The energy is calculated as an expansion in decreasing powers of the cluster radius, R∝N1/3. Contributions of volume (R3), surface (R2), curvature (R), constant (R0), (1/R), and (1/R2) are clearly separated in the formula. Chemical potentials, fusion and fission potentials, surface thickness, and unit radii are also obtained. [ABSTRACT FROM AUTHOR]