"How PhAI Decodes X-Ray Phases in Crystals"

A team of scientists has introduced an innovative technique for analyzing the dynamics of microscopic interacting particles through image recognition. This method allows for counting particles within an adjustable imaginary box, enabling researchers to study collective behavior even in dense fluid suspensions. Their findings have been published in Physical Review X.

For over a century, particle counting has intrigued scientists across various fields, including biology, chemistry, and physics, particularly regarding Brownian motion in liquids. A vital measure in this context is the diffusion constant, which reflects the average movement speed of particles. Traditionally, this constant is determined by tracking individual particles, but this can be challenging in dense systems.

To address these limitations, Sophia Marbach and her team from Sorbonne Université developed the "countoscope." This device uses image recognition software to efficiently count large numbers of particles in selected observation boxes, ranging from a few to thousands, depending on the research needs.

In their experiments, the researchers tested the technique on a two-dimensional layer of plastic spheres in water, using custom-built equipment to image and count particles in square boxes of various sizes. They found that the average change in particle numbers increased proportionally to the square root of time, allowing them to accurately calculate the diffusion constant.

As particle density increased, they observed expected diffusion behavior but also noted the formation of temporary clusters of particles, a phenomenon overlooked in traditional studies that focus on individual tracking. This indicates that their method can reveal new dynamics in particle interactions.

While their model used non-interacting particles, the team recognized that real-world systems often involve significant interactions. They adjusted their mathematical analysis to accommodate both hydrodynamic and steric effects, discovering a new length scale that characterizes transitions between different particle behaviors.

The researchers are optimistic about extending their methodology to three-dimensional systems and other materials like solids and crystals. Marbach noted growing interest from fellow scientists, emphasizing the simplicity and versatility of the countoscope for studying a range of systems, including microalgae, bacteria, and active colloids. This opens up exciting avenues for future research into various dynamical features beyond diffusion.