Skip to Content
Uncategorized

Contaminants Can Flow Up Waterfalls, Say Physicists

Physicists have discovered an entirely new process of upstream contamination–by studying the behaviour tea leaves

Here’s a curious phenomenon.

The south American drink ‘mate’ is a tea-like beverage in which finely cut, dried leaves from the yerba mate herb are infused in hot water. The dried leaves, just a few square mm in size, tend to float on the surface of the water

While pouring the hot water onto the leaves, Ernesto Althsuler and buddies at the University of Havana in Cuba, noticed a puzzling phenomenon. They found that, sometimes, the leaves would somehow travel upstream and end up contaminating the upstream container of pure water.

Being diligent physicists, they decided to investigate. They found that the leaves (and also chalk powder) were able to navigate upstream if the waterfall was less than about a centimetre in height. “For distances of the order of 1 cm or less, some of the floating particles eventually start to “climb up the stream”,” they say.

How can this be? Altshuler and co say the geometry of the system is important. Their set up consists of a relatively long horizontal channel, along which the water flows, followed by a short drop into the infusion (see diagram above).

In the past, physicists have observed vortices in horizontal flows which can set up a counterflow. When this happens, there is a main flow through the middle of the channel and a counterflow along the edges, which can carry small particles in the opposite direction.

What’s new, however, is the idea that the vortices can survive the drop and continue to generate a counterflow even after the water has plunged over the lip of the channel.

Altshuler and co think that this counterflow lifts particles out of the lower container and pumps them back into the upper container. But only if the drop is not too big–less than a centimetre or so.

That’s an interesting effect that you could probably recreate in your kitchen.

But it’s more than a mere curiosity. Altshjuler and co say their discovery “may have potential implications in many chemical, medical, pharmaceutical and industrial processes.”

So if you’re mixing processes are plagued by problems of contamination, perhaps the “mate” effect is to blame.

Ref: arxiv.org/abs/1105.2585: Upstream Contamination In Water Pouring

Deep Dive

Uncategorized

Embracing CX in the metaverse

More than just meeting customers where they are, the metaverse offers opportunities to transform customer experience.

Identity protection is key to metaverse innovation

As immersive experiences in the metaverse become more sophisticated, so does the threat landscape.

The modern enterprise imaging and data value chain

For both patients and providers, intelligent, interoperable, and open workflow solutions will make all the difference.

Scientists have created synthetic mouse embryos with developed brains

The stem-cell-derived embryos could shed new light on the earliest stages of human pregnancy.

Stay connected

Illustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.