arXiv subjects

Danilo S. Borges

Publications and source records attributed to Danilo S. Borges.

3 recordsLinked to original sources

arXiv2025

Role of Friction on the Formation of Confined Granular Structures

Unstable systems of fluidized grains in a very-narrow vertical tube can auto-defluidize after some time, the settling particles forming either a glass- or crystal-like structure. We carried out experiments using different polymer spheres, of known friction and roughness, fluidized in water. A diagram was obtained for the \RefereeA{shell-settled} particles when the coefficient of friction is of the order of 0.1, and their structure is characterized through an analysis of the nearest neighbors' angles. We show that the level of velocity fluctuations is higher for the high friction material, and that, once defluidized, the decrease in the coefficient of sliding friction leads to more organized (crystal-like) structures, while those with higher friction coefficients are amorphous (glass-like structures). Our results bring new insights for understanding the formation of glass- and crystal-like structures based on the material surface properties.

cond-mat.soft↗

arXiv2025

Resultant force on grains of a real sand dune: How to measure it?

Dunes are bedforms found on sandy terrains shaped by fluid flow on Earth, Mars, and other celestial bodies. Despite their prevalence, understanding dune dynamics at the grain scale is challenging due to the vast number of grains involved. In this study, we demonstrate a novel approach to estimate the forces acting on individual dune grains using images. By combining subaqueous experiments, high-speed camera recordings, discrete numerical simulations, and a specially trained convolutional neural network, we can quantify these forces with high accuracy. This method represents a breakthrough in studying granular dynamics, offering a new way to measure forces not only on dune grains but also on smaller objects, such as rocks, boulders, rovers, and man-made structures, observed in satellite images of both Earth and Mars. This technique expands our ability to analyze and understand fluid-grain interactions in diverse environments.

physics.geo-ph↗

arXiv2021

Morphological transition between patterns formed by threads of magnetic beads

Magnetic beads attract each other forming chains. We pushed such chains into an inclined Hele-Shaw cell and discovered that they spontaneously form self-similar patterns. Depending on the angle of inclination of the cell, two completely different situations emerge, namely, above the static friction angle the patterns resemble the stacking of a rope and below they look similar to a fortress from above. Moreover, locally the first pattern forms a square lattice, while the second pattern exhibits triangular symmetry. For both patterns, the size distributions of enclosed areas follow power laws. We characterize the morphological transition between the two patterns experimentally and numerically and explain the change in polarization as a competition between friction-induced buckling and gravity.

cond-mat.stat-mech↗