porous material

After the Big Bang, according to inflationary cosmology, the Universe underwent rapid expansion and a series of phase transitions.

The brain self-cleans its waste: cerebrospinal fluid flows through narrow channels surrounding arteries. The channel walls are soft and ripple with each pulse, and the tissue is porous like a sponge. Every heartbeat turns arteries into tiny pumps, driving fluid through the pores.

Soil is not a solid sponge but a labyrinth of pores of various sizes. After rain, water does not fill them all at once: first the narrowest ones, then the wider ones. Physicists built a theory of this process based on a simple image — a set of communicating vessels.

Millions of cilia, thin hairs, work inside the tiny ducts of our bodies. They beat in synchrony, like the oars of a galley, pushing viscous mucus or fluid along. The authors of a new study propose viewing the ciliary carpet as an active porous medium — something like a sponge that squeezes and releases itself, driving water through.

A porous implant filled with a drug works like a sponge that slowly releases the substance into the surrounding fluid. But if the fluid flows quickly, it washes out the drug differently than in a calm environment. The authors computed on a computer how different flow rates and properties of the porous structure affect drug release.

In porous materials (soil, rocks, filters) fluids move through tiny, winding channels. When two immiscible fluids, such as water and air, are present simultaneously, their interface constantly shifts: air bubbles push water out of some pores and open paths through others.

In a narrow gap between two plates, water from humid air collects on its own: this is capillary condensation. If the gap is only a few nanometers wide, water no longer behaves like a continuous liquid: every molecule counts.

Inside the kidneys, liver, and other organs, fluid flows through channels that squeeze and release like a hose underfoot. The walls of these channels are not rigid: they are porous, elastic, and soaked with moisture.

A flat sheet with slits in a flow of water or air behaves like self-adjusting blinds. The pressure opens the gaps, and each strip of material tilts, turning into a miniature wing. Thus, even a sheet placed perpendicular to the flow generates not only drag but also significant lateral lift.

A rod stuck into a granular material (say, sand or a layer of small beads) behaves quite differently from what you might expect. Instead of going straight down, it quickly tilts away from the vertical and ends up lying flat. That's what researchers found when they dropped rigid and flexible rods into a two-dimensional layer of foam beads and tracked their motion with a high-speed camera.

Felt looks like a tangled ball of wool, but under X-rays you can see hidden trails inside. When a water drop lands on such material, it doesn't just spread across the surface — some of the liquid dives deep, like water into blotting paper. Scientists captured this process for the first time with an X-ray camera snapping hundreds of frames per second. The secret lies in the needles.

Inside a fuel cell, protons must race through a solid material like commuters through turnstiles at rush hour. If the turnstiles are sparse and narrow, the current is weak. In the past, to find a material with good proton conductivity, chemists had to screen compounds almost blindly, one by one.

When two tectonic plates grind against each other, a layer of pulverized rock ends up between them, like sand between your palms. This layer, which geologists call fault gouge, behaves not like solid rock but like a thick paste: it can compact, dilate, and slide. Whether a fault ruptures in a devastating earthquake or creeps slowly and safely depends on its whims.

Pour a handful of dry sand: it will spread into a neat cone. Now grab a box of star-shaped pasta: the pile will stand almost vertical. Why? It's all about particle shape. Physicists built cylindrical piles from particles of different geometries — from smooth spheres to 'polypods' with several arms, like a sea star.

Drop honey onto a sponge. It lazily creeps, avoiding the voids. But if the honey becomes thinner under pressure, the flow gets trickier. Liquid with variable thickness in an uneven labyrinth of pores — a problem that had defied calculation. The authors of the new work averaged the chaos of microchannels into simple equations.