Grupo SPhinX

Finite-Range Attractions Reveal Hidden Structure in a Simple One-Dimensional Fluid

A new study shows that even a seemingly simple one-dimensional model of particles that can stick together in pairs can display unexpectedly rich behavior - and reveals precisely where a widely used theory succeeds and fails. The particles are hard rods with attractive ends, which form reversible chains. The researchers exploit an exact solution of the corresponding one-dimensional fluid to test Wertheim's theory, a standard approach for describing how particles associate. They find that the theory is exact when the attractive interaction is infinitely short-ranged, but misses important effects when attraction extends over a finite distance. By reformulating the exact solution in terms of the quantities used by the theory, they identify how it can be corrected exactly in one dimension. The finite range of attraction also produces previously unseen structural behavior: correlations between particles can change from a smooth to an oscillatory decay, and the characteristic distance over which particles remain correlated can develop several distinct extrema. At very high pressure, the correlation length grows differently for finite-range and infinitely short-range attractions. These results provide an exact benchmark for association theories and show how subtle changes in the range of an interaction can profoundly alter collective behavior.

Link to the paper: https://doi.org/10.1063/5.0344388

Granular materials such as sand, powders, and grains often behave in unexpected ways when they flow. Unlike ordinary fluids, their particles lose energy in collisions and can also rotate because of surface roughness, making their collective behavior extremely difficult to predict. In this work, the authors develop the first exact theoretical description of a steadily sheared granular gas that simultaneously accounts for both effects. Using a simplified but remarkably powerful kinetic model, they derive explicit mathematical expressions for the stresses, energy distribution, and other quantities that characterize the flow without resorting to numerical simulations or uncontrolled approximations. The results reveal how particle roughness fundamentally modifies the flow properties and identify several unexpected nonlinear effects, including optimal roughness conditions that maximize or minimize important rheological properties. Besides providing new physical insight into granular matter far from equilibrium, the exact solution establishes a benchmark against which approximate theories and computer simulations can be tested. More broadly, it expands the very limited class of nonequilibrium many-particle systems whose behavior can be determined exactly, offering new tools for understanding complex materials driven far from thermal equilibrium.

Link to the paper: https://doi.org/10.1007/s10955-026-03675-2

Congratulations to 𝐀𝐧𝐚 𝐌. 𝐌𝐨𝐧𝐭𝐞𝐫𝐨, on receiving the award for “𝐁𝐞𝐬𝐭 𝐎𝐫𝐚𝐥 𝐏𝐫𝐞𝐬𝐞𝐧𝐭𝐚𝐭𝐢𝐨𝐧 𝐨𝐧 𝐓𝐡𝐞𝐨𝐫𝐞𝐭𝐢𝐜𝐚𝐥 𝐏𝐡𝐲𝐬𝐢𝐜𝐬” at the SigmaPhi Conference, held in Kolymbari, Crete. 🇬🇷

This award is a well-deserved recognition of the quality of her research and presentation. We are very happy to celebrate this achievement with her.

Well done, Ana! 👏🔬

🔎📖𝐋𝐚𝐩𝐥𝐚𝐜𝐞 𝐩𝐨𝐥𝐞𝐬 𝐜𝐚𝐧 𝐫𝐞𝐯𝐞𝐚𝐥 𝐡𝐢𝐝𝐝𝐞𝐧 𝐨𝐫𝐝𝐞𝐫 𝐢𝐧 𝐜𝐫𝐨𝐰𝐝𝐞𝐝 𝐡𝐚𝐫𝐝 𝐫𝐨𝐝𝐬 📖🔎

How do particles organize when space is almost gone? In dense one-dimensional hard-rod systems, tiny gaps between particles still encode long-range structural information. Our work uses Laplace-transform pole analysis to describe the radial distribution function at high packing fractions, revealing how spatial correlations decay and oscillate as the system approaches its crowded limit.
🟡🟢🔵
The result is a compact theta-function representation that captures both key regimes: an intermediate algebraic decay and a long-distance exponential relaxation. Beyond the classic Tonks gas, the same framework extends naturally to binary mixtures and confined quasi-one-dimensional hard-disk geometries, offering a unified view of correlations in crowded systems.
🟡🟢🔵
A simple pole structure in complex space becomes a clear physical picture of order, decay, and confinement.

Link to the article: doi.org/10.1103/gcyg-yw98

Last Friday, June 19, 2026, our group celebrated a very special workshop (https://fisteor.cms.unex.es/workshop-tribute/) in tribute to the remarkable scientific careers of Andrés Santos and Vicente Garzó, who are retiring at the end of this academic year.

Colleagues, collaborators, and former PhD students came together for a truly memorable and emotional day — a heartfelt farewell to two exceptional scientists and mentors.

Andrés and Vicente, you will be deeply missed. Thank you for everything!

🌟𝐍𝐞𝐰 𝐫𝐞𝐯𝐢𝐞𝐰: 𝗘𝘅𝗽𝗹𝗼𝗿𝗶𝗻𝗴 𝘁𝗵𝗲 𝗗𝘆𝗻𝗮𝗺𝗶𝗰𝘀 𝗼𝗳 𝗖𝗼𝗻𝗳𝗶𝗻𝗲𝗱 𝗚𝗿𝗮𝗻𝘂𝗹𝗮𝗿 𝗙𝗹𝘂𝗶𝗱𝘀🌟

This review explains how a simple theoretical model can describe the surprising behavior of granular materials - collections of macroscopic particles such as sand, grains, or powders - when they are confined in a shallow vibrating box. Unlike ordinary fluids, these systems constantly lose energy during collisions, so they must be continuously driven to keep moving. The work reviewed here focuses on a model that captures how vertical vibrations inject energy into the particles and redistribute it through collisions, allowing the system to remain active and fluid-like. The importance of this model is that it turns a very complicated experimental setup into a mathematically tractable problem while still reproducing many observed behaviors.

The review summarizes how kinetic theory can predict key properties of these driven granular systems, including their steady states, transport properties, and stability. It also shows how the model successfully describes mixtures of different particles, where unusual nonequilibrium effects appear, such as unequal sharing of energy between species and spontaneous segregation. More recent studies discussed in the review reveal that the same framework can also explain exotic phenomena including quasicrystal formation, long-range order, and unusual collective phases in driven matter.

📘📘
𝑫𝒚𝒏𝒂𝒎𝒊𝒄 𝑷𝒓𝒐𝒑𝒆𝒓𝒕𝒊𝒆𝒔 𝒊𝒏 𝒂 𝑪𝒐𝒍𝒍𝒊𝒔𝒊𝒐𝒏𝒂𝒍 𝑴𝒐𝒅𝒆𝒍 𝒇𝒐𝒓 𝑪𝒐𝒏𝒇𝒊𝒏𝒆𝒅 𝑮𝒓𝒂𝒏𝒖𝒍𝒂𝒓 𝑭𝒍𝒖𝒊𝒅𝒔: 𝑨 𝑹𝒆𝒗𝒊𝒆𝒘
Link to the review in 𝙀𝙣𝙩𝙧𝙤𝙥𝙮.
https://www.mdpi.com/1099-4300/28/4/454
📘📘

🔬𝐖𝐡𝐞𝐧 𝐝𝐮𝐦𝐛𝐛𝐞𝐥𝐥𝐬 𝐭𝐞𝐚𝐜𝐡 𝐮𝐬 𝐛𝐢𝐠 𝐥𝐞𝐬𝐬𝐨𝐧𝐬 𝐚𝐛𝐨𝐮𝐭 𝐨𝐫𝐝𝐞𝐫 🔵🟠🟣

❓ What happens when microscopic “dumbbell-shaped” particles are squeezed into an ultra-narrow line where they can barely move but can still rotate?

Our work reveals something fascinating: these particles spontaneously organize themselves into surprisingly complex patterns, purely because of geometry and entropy. At low density, the particles point in many directions almost randomly. But as the system becomes crowded, they begin to “choose” preferred orientations, forming two dominant alignment directions — a kind of collective behavior emerging between particles.

We also uncovered long-range correlations and hidden ordering effects due to the interplay between positional and orientational correlations that resemble behaviors seen in liquid crystals, biological systems, and confined materials.

𝙒𝙝𝙮 𝙙𝙤𝙚𝙨 𝙞𝙩 𝙢𝙖𝙩𝙩𝙚𝙧❓
Because understanding how simple shapes self-organize under confinement can help scientists design:
🧪 smarter soft materials
📦 better nanoparticle packing systems
🧬 improved models for biological transport in narrow channels
⚙️ future nanotechnology and microfluidic devices

This work shows how complexity can emerge from incredibly simple rules — one of the most beautiful ideas in physics.

📄 Link to the article in 𝑷𝒉𝒚𝒔𝒊𝒄𝒂𝒍 𝑹𝒆𝒗𝒊𝒆𝒘 𝑬: https://journals.aps.org/pre/abstract/10.1103/sdt7-t224

El pasado 22 de abril celebramos el acto de 𝑺𝒂𝒏𝒕𝒐 𝑻𝒐𝒎𝒂́𝒔 𝒅𝒆 𝑨𝒒𝒖𝒊𝒏𝒐 en la Universidad de Extremadura, un evento muy especial para nuestra comunidad académica.

En él, nuestros antiguos doctorandos y actuales investigadores postdoctorales del grupo, 𝗝𝗲𝘀𝘂́𝘀 𝗠𝗮𝗿𝗶́𝗮 𝗠𝗮𝗿𝗰𝗼𝘀 𝗠𝗲𝗿𝗶𝗻𝗼 𝘆 𝗔𝗻𝗮 𝗠𝗮𝗿𝗶́𝗮 𝗠𝗼𝗻𝘁𝗲𝗿𝗼 𝗠𝗮𝗿𝘁𝗶́𝗻𝗲𝘇, recibieron oficialmente el Premio Extraordinario de Doctorado.

Un reconocimiento más que merecido a su esfuerzo, dedicación y excelencia investigadora 👏

¡Enhorabuena a ambos!

𝐃𝐞𝐬𝐜𝐚𝐫𝐭𝐞𝐬’ 𝐂𝐞𝐧𝐭𝐮𝐫𝐢𝐞𝐬-𝐎𝐥𝐝 𝐈𝐝𝐞𝐚 𝐇𝐞𝐥𝐩𝐬 𝐄𝐱𝐩𝐥𝐚𝐢𝐧 𝐖𝐡𝐲 𝐇𝐨𝐭 𝐂𝐚𝐧 𝐂𝐨𝐨𝐥 𝐅𝐚𝐬𝐭𝐞𝐫 🔥🌡️❄️

Hot water can sometimes cool faster than cold—a surprising effect that has puzzled scientists for decades. In this work, we show that this phenomenon can be understood and precisely controlled by combining a modern “memory-based” model of cooling with a little-known idea that dates back to René Descartes. His proposed thermal setup, involving three different temperature reservoirs, turns out to provide a powerful way to uncover when and how this effect occurs.

In standard explanations, the Mpemba effect is often linked to complex physical mechanisms. Here, we show instead that it can arise even in a simple model of cooling, as long as the system retains a short memory of its past. Building on this, we analyze a protocol inspired by Descartes in which two samples, initially at different temperatures (hot and warm), are quenched to a common cold reservoir at different times. This three-reservoir arrangement allows us to clearly separate the roles of timing and temperature in the cooling process.

What is new in our work is a complete analytical description of the conditions under which the effect appears, how strong it can be, and how to optimize it. We also find that adding this extra reservoir does not necessarily make the effect stronger than in simpler setups.

By linking a historical idea with modern theory, our results highlight how the path taken—not just the starting point—governs how systems cool.

Link to the article in 𝑱𝒐𝒖𝒓𝒏𝒂𝒍 𝒐𝒇 𝑷𝒉𝒚𝒔𝒊𝒄𝒔 𝑨: https://iopscience.iop.org/article/10.1088/1751-8121/ae57ed

𝐍𝐞𝐰 𝐭𝐡𝐞𝐨𝐫𝐲 𝐩𝐫𝐞𝐝𝐢𝐜𝐭𝐬 𝐡𝐨𝐰 𝐬𝐡𝐚𝐤𝐞𝐧 𝐠𝐫𝐚𝐢𝐧 𝐦𝐢𝐱𝐭𝐮𝐫𝐞𝐬 𝐟𝐥𝐨𝐰 𝐚𝐧𝐝 𝐬𝐞𝐩𝐚𝐫𝐚𝐭𝐞 𝐢𝐧 𝐭𝐢𝐠𝐡𝐭 𝐬𝐩𝐚𝐜𝐞𝐬 🔵🔴🟢

Granular materials can behave in surprising ways when particles of different sizes are confined between two close plates and continuously shaken. In this paper, we developed a general theory that predicts how such mixtures move, resist deformation, and separate under those conditions, even when the particles are already fairly crowded. Earlier studies could usually treat only very dilute mixtures or special cases, such as when one component was present in tiny amounts. The new result here is a broader description for mixtures with arbitrary composition at moderate density, together with explicit formulas for key transport properties and a criterion that tells us when larger grains tend to accumulate near the colder side and when they instead migrate toward the hotter side. This is important because the tendency of granular mixtures to mix or segregate affects many natural and industrial systems, from powders and grains to processing technologies that rely on particulate materials. By turning a complicated many-particle problem into a practical predictive framework, our work helps clarify how confinement, dissipation, density, and particle differences combine to control the behavior of vibrated granular mixtures.

Link to the article in 𝘗𝘩𝘺𝘴𝘪𝘤𝘴 𝘰𝘧 𝘍𝘭𝘶𝘪𝘥𝘴: https://doi.org/10.1063/5.0321569