Ariday S. Mosquera Polo

We show that, under specific conditions, a lighter object can reach a higher terminal velocity than a heavier one when falling through a highly dense and viscous fluid. This counterintuitive result, obtained within the regime where Stokes' law applies, challenges the common assumption that heavier objects fall faster. While it is well known that compact objects fall at similar rates in air regardless of mass, and that heavier objects typically fall faster when lighter ones are more extended, the behavior in denser and more viscous media has been less explored. We analyze spheres with different densities and radii falling in such a medium, considering gravitational, buoyant, and drag forces, and assuming no interaction between them. Depending on the radius ratio, the denser sphere may reach a higher terminal velocity and touch the ground first-whether it is heavier, lighter, or equal in weight to the other. Interestingly, when the less dense sphere has the higher terminal velocity, it is always the heavier one; however, whether it lands first also depends on the initial height. These findings provide new insights into low-Reynolds-number dynamics, with potential applications in education, experimental design, and engineering.

We investigate the impact of normal linear strips—both perpendicular and parallel to the direction of vortex motion—on the dynamics of fractional vortices in a two-band superconducting slab. In the absence of pinning, composite vortices dominate throughout the sample, while non-composite (dissociated) vortices appear only near the vortex entry edge, with energy dissipation primarily governed by the motion of composite structures. To modulate vortex behavior, we introduce linear regions of locally suppressed superconductivity, oriented either perpendicular or parallel to the vortex trajectory. A single perpendicular strip confines fractional vortices to the injection region, whereas two perpendicular strips stabilize composite vortices in the central domain and induce fractional vortex states near the boundaries. In contrast, parallel strips promote the dissociation of vortices across the entire sample, significantly altering the spatial configuration and dynamics of the vortex matter. Furthermore, the interband correlation coefficient serves as a direct indicator of the degree of spatial overlap between vortices in the two condensates. These findings highlight the critical role of pinning geometry in shaping vortex dynamics and energy dissipation, offering new strategies for controlling flux behavior in multiband superconductors for technological applications.

This study examines the dynamics of two spheres falling independently in a viscous fluid, highlighting conditions under which a lighter sphere can achieve a higher velocity than a heavier one. Through theoretical modeling and simulations, the motion of spheres with varying densities and radii, released simultaneously in a uniform viscous medium, was analyzed. The investigation considers gravitational, buoyant, and drag forces, with the spheres moving under identical initial conditions and without mutual interaction. The results confirm the well-established case where the heavier sphere exhibits a greater terminal velocity. However, an intriguing phenomenon is identified: under specific conditions, a lighter sphere can surpass its counterpart in terminal velocity. Additionally, when spheres of equal weight are compared, the denser sphere consistently attains a higher terminal velocity. The study reveals non-trivial time-dependent acceleration patterns, with alternating dominance between heavier and lighter spheres before terminal velocities are reached. Furthermore, the order of impact with the ground is shown to depend on the release height, illustrating a complex interplay of forces. These findings offer novel insights into fluid dynamics, with implications for education and engineering applications.

In this study, we employed the Pearson product-moment correlation coefficient ([ ]) to identify non-composite vortex states in a two-band superconducting slab. The fractional vortices were simulated using the two-component Ginzburg–Landau equations TDGL, with the link variable method and the healing coupling between the superconducting bands. The coefficient [ ] was calculated based on the square modulus of the order parameters of the two condensates, providing insight into the correlation between the two bands. Statistically, [ ] ranges from [ ]1 to 1, where values approaching 1 indicate composite vortices, while values nearing 0 suggest non-composite vortices. In this context, negative values of [ ] are irrelevant. The use of this tool enabled us to assess the degree of decoupling (coincidence of the position of the vortex centers in the superconducting bands) within the vortex lattice, allowing for the identification of specific fields and currents associated with the uncoupled vortex states in the superconducting slab. Such findings are crucial for managing energy dissipation in multi-band superconducting materials and manipulation of the vortices state in multi-band superconducting system.

En el presente trabajo se utilizó el código Wien2k, en el marco de la teoría del funcional de la densidad de Kohn-Sham, aplicando el método de ondas planas aumentadas y linealizadas (full-potential linearized augmented plane wave, FP- LAPW) y adoptando la aproximación de gradiente generalizado (GGA) de Perdew, Burke y Ernzerhof para la energía de intercambio y correlación, así como la aproximación de densidad local (local density approximation, LDA) para el cálculo de la densidad de estados y la estructura de bandas de la perovskita doble Sr2HoNbO6. Para los cálculos se consideró el grupo Fmm (#225), experimentalmente obtenido a partir de mediciones de difracción de rayos X y del método de refinamiento de Rietveld. El parámetro de red experimental fue de 8.018 Å, el cual concuerda en un 99,2 % con las predicciones teóricas efectuadas a partir de la minimización de la energía mediante la ecuación de estado de Murnaghan. A partir de mediciones de susceptibilidad magnética en función de la temperatura y del ajuste con la ley de Curie, se obtuvo el valor del momento magnético efectivo 10,01 μB. Este valor es muy cercano del esperado teóricamente a partir de las reglas de Hund (10,60 μB). La brecha de energía determinada entre las bandas de valencia y de conducción fue de 3,3 eV, lo que revela el carácter aislante de la perovskita compleja Sr2HoNbO6 para la configuración de espín hacia arriba, en tanto que se observó el carácter semiconductor para la polarización de espín hacia abajo, con una brecha de energía de 0,77 eV. Las propiedades termodinámicas se calcularon a partir de la ecuación de estado usando el modelo cuasi-armónico de Debye. Un comportamiento del calor específico, con CV≈CP, se encontró a temperaturas inferiores a T = 500 K, con valores del límite de Dulong-Petit que doblaban los que se han reportado para materiales del tipo de la perovskita. © 2018. Acad. Colomb. Cienc. Ex. Fis. Nat.