Researchers Pore Over the Physics Behind the Layered Latte

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The layered latte isn't the most widely known espresso drink on coffee-shop menus, but it is a scientific curiosity. Instead of a traditional latte, where steamed milk is poured into a shot (or several) of espresso, the layered latte is made by pouring the espresso into a glass of hot milk. The result is an Instagram-friendly drink that features a gradient of milky coffee colors from pure white on the bottom to dark brown on the top. The effect is odd enough that Princeton University researchers decided to explore the fluid dynamics that make it happen, as The New York Times reports.

In a new study in Nature Communications, Princeton engineering professor Howard Stone and his team explore just what creates the distinct horizontal layers pattern of layered latte. To find out, they injected warm, dyed water into a tank filled with warm salt water, mimicking the process of pouring low-density espresso into higher-density steamed milk.

Four different images of a latte forming layers over time
Xue et al., Nature Communications (2017)

According to the study, the layered look of the latte forms over the course of minutes, and can last for "tens of minutes, or even several hours" if the drink isn't stirred. When the espresso-like dyed water was injected into the salt brine, the downward jet of the dyed water floated up to the top of the tank, because the buoyant force of the low-density liquid encountering the higher-density brine forced it upward. The layers become more visible when the hot drink cools down.

The New York Times explains it succinctly:

When the liquids try to mix, layered patterns form as gradients in temperature cause a portion of the liquid to heat up, become lighter and rise, while another, denser portion sinks. This gives rise to convection cells that trap mixtures of similar densities within layers.

This structure can withstand gentle movement, such as a light stirring or sipping, and can stay stable for as long as a day or more. The layers don't disappear until the liquids cool down to room temperature.

But before you go trying to experiment with layering your own lattes, know that it can be trickier than the study—which refers to the process as "haphazardly pouring espresso into a glass of warm milk"—makes it sound. You may need to experiment several times with the speed and height of your pour and the ratio of espresso to milk before you get the look just right.

[h/t The New York Times]

Some People Can Control When They Get Goosebumps—and Scientists Are Stumped

This woman might be controlling her goosebumps with her mind.
This woman might be controlling her goosebumps with her mind.
MyetEck/iStock via Getty Images

Travis Carrasco, 29, is a mechanical engineer in Las Vegas, Nevada. For all intents and purposes, he’s a normal individual. He loves coloring with colored pencils; likes leadership books and the color green.

But in youth, his relatives took notice of Carrasco’s peculiar tendency to sway his head back and forth. He told them he was giving himself goosebumps. They didn’t believe him.

They were wrong.

According to the low end of informal estimates, about one in every 1500 people have something called Voluntarily Generated Piloerection (VGP)—the ability to consciously give themselves goosebumps. The weird thing is, VGP shouldn’t exist. The phenomenon both perplexes and intrigues neurophysiologists by defying conventional understanding of how the unconscious nervous system operates.

A mammal’s hair follicle clings to the skin via a tiny muscle. When this muscle contracts, the hair will stand, the skin around it will undergo bump-shaped distortion, and voilagoosebumps.

For the 1499 people in this statistical metaphor, goosebumps are completely involuntary. The tiny muscle, called the arrector pili, is made of smooth muscle fibers. And like other smooth muscles of the body—those that handle digestion, blood flow, respiration, and so on—they are unconsciously regulated. The nerves attached to them lie in the autonomic nervous system, the part of the nervous system dedicated to managing bodily functions you aren’t supposed to control consciously, like heart rate or pupil dilation.

Voluntary Generated Piloerection "Shouldn't Be Possible"

When James Heathers, a physiologist at Northeastern University, came across an engineering paper referencing the only three single-individual case studies of VGP in medical history, he couldn’t believe it. 

“That was catnip for me,” Heathers tells Mental Floss, his voice cracking with excitement. “[VGP] shouldn’t be possible. That’s not how the autonomic nervous system works; what it does. This reason that it’s called autonomic—autonomos—it means ‘without thought.’”

Heathers, who normally spends his time in data science and patient-centered electronic health development, got to work on goosebumps as a scientific side-hustle. In 2018, he authored a paper in the journal PeerJ making the first published attempt at defining the prevalence and properties of VGP.

He wanted to know exactly how it works. What do people think about when they give themselves goosebumps? In what situations are they deployed? What personality traits are common in people with VGP?

Heathers sifted through obscure internet forums and sent out surveys, and ended up evaluating 32 participants with VGP using standardized personality tests. He found that those with VGP who responded to his survey had unusually ‘open’ personalities compared to the average person.

“They seem to be more creative; they imagine more,” Heathers says. “They pay more attention to themselves. They track their emotions more closely. They have a preference for new stuff … That’s either an artifact of people who are more open being more likely to answer a survey on the internet for fun, because they want to know about themselves; or it’s a component of the experience itself.”

A "Sixth Sense"

You may be thinking, Wait, I’m open-minded, and I can give myself goosebumps just by thinking of nails scratching a chalkboard. But Heathers is clear; that’s not VGP. 

“VGP has no mental or cognitive component,” Heathers says. “The vast majority of people who do it, in the way that we’ve defined it, simply have a really straightforward pathway. A lot of the time, they focus on a point, behind their ear or on their neck or at the back of the head. They don’t have to think of anything.”

In other words, those with VGP need only think about getting goosebumps—not about the situations that would, under normal circumstances, give them goosebumps.

“Basically, it starts at the base of my neck, the bottom of my head and the backside,” Carrasco, the engineer with VGP, tells Mental Floss. “When I trigger it, it feels like a bunch of sparks travel throughout my entire body, and I can do it repetitively, over and over and over and over and over. However, the strongest sensation is only the first couple times.”

While the induced goosebumps are stronger than those generated unconsciously, Carrasco says he can maximize the strength and resolution of his goosebumps by swaying his head from side to side.

“It’s a weird rhythm, but if I sway my neck, it triggers a really strong response,” Carrasco says. “You know when you squeeze your eyes really tight, and sometimes you hear pressure building, and it’s really just squeezing a muscle in your ears or your eyes. It’s similar to that, but when [the goosebumps] happen, sometimes I can hear that same pressure … it feels relaxing. It feels good.”

Carrasco likes to think it’s a sixth sense. He’s never met anyone else with VGP. But he notices that his son of 19 months sways his head a lot, too. And Carrasco can’t help but wonder, “Does he have the same ability I have?”

Maybe it’s genetic; scientists don't know. Whatever the cause, 30 to 40 times a week, you’ll catch Carrasco exercising his hidden superpower—a thought that just might give you goosebumps.

10 Citizen Science Projects That Need Your Help

A citizen scientist takes a photo of scarlet mushrooms.
A citizen scientist takes a photo of scarlet mushrooms.
lovelypeace/iStock via Getty Images

Channel your inner Nikola Tesla or Marie Curie by participating in actual scientific research, either out and about or without even leaving your couch. These projects unleash the power of the public to be places that researchers can’t be and to spread the workload when data start piling up. They really can’t do it without you.

1. Catalog photos of Earth's cities at night.

Photo from space of a city at night
Identify cities from the photos taken from the International Space Station.
Chris Hadfield, NASA // Public Domain

Cities at Night—a study by Complutense University of Madrid—asks people to catalog images of the Earth at night taken from the International Space Station, part of the millions of images in the Gateway to Astronaut Photography of Earth database. The current project, Lost at Night, needs people to identify cities within images of 310-mile circles on Earth. Hundreds of volunteers have classified thousands of images already, but classification by multiple individuals ensures greater accuracy. In fact, the project will determine the optimum number of people needed. The primary goal is an open atlas of publicly available nighttime images. Just log on to the image database to help.

2. Follow fish using high-tech tags.

You’ll have to go fishing—an outdoor activity you can do by yourself!—for this assignment. Volunteer to tag fish for the American Littoral Society, whose citizen scientists have tagged more than 640,000 fish since the program began in 1965. You can tag the fish you catch and release, or report tagged fish to the organization. The data is sent to the National Marine Fisheries Service Laboratory in Woods Hole, Massachusetts, where it helps scientists track the populations and movements of coastal species like striped bass, flounder, and bluefish. To get started, become a member of the American Littoral Society, which comes with a packet of tagging gear and instructions.

3. Spy on penguins in Antarctica.

Penguins on an ice floe
Keeping tabs on penguins is one way a citizen scientist can lend a hand.
axily/iStock via Getty Images

Here's another project for those stuck indoors. Penguins are threatened by climate change, fisheries, and direct human disturbance, yet scientists have little data on the birds. To fill in the gaps, 50 cameras throughout the Southern Ocean and Antarctic Peninsula take images of colonies of gentoo, chinstrap, Adélie, and king penguins year-round. You can help the University of Oxford-based research team by sorting through thousands of images to identify and mark individual adult penguins, chicks, and eggs. You'll be pinpointing seasonal and geographic variations in populations that may represent changes to the Antarctic ecosystem. Marking other animals in the images helps researchers figure out which ones are hanging around penguin colonies. Discuss a specific image or the project with the science team and other volunteers in an online forum.

4. Battle an invasive marine species.

Like to dive or snorkel? Make it count by reporting lionfish sightings or captures to the Reef Environmental Education Foundation's Volunteer Reef Survey Project. Lionfish, which are native to the Indo-Pacific, were first sighted in the South Atlantic in 1985 and were likely released by private aquarium owners. Since then, they have spread throughout the Caribbean and Gulf of Mexico and caused native fish populations to decline by up to 80 percent. Scientists say this invasion may be one of the century’s greatest threats to warm temperate and tropical Atlantic reefs. You can also join a lionfish derby to catch and kill some of the tasty fish so scientists can analyze their biology.

5. Count birds from your backyard.

Bluebirds at a bird feeder
Bluebirds dine on mealworms at a bird feeder.
MelodyanneM/iStock via Getty Images

North American birds are in trouble. Recent studies predict dramatic declines in the populations of migratory birds due to climate change—and much of the data that went into these studies came from citizen scientists who monitored species without leaving home. The Cornell Lab of Ornithology and Birds Canada launches Project FeederWatch in the winter months; you simply put out a bird feeder and report the number and species of birds that visit it. Citizen scientists can also join the Cornell Lab's NestWatch—you find a nest, monitor it every three or four days, and report your data. And every February, the Audubon Society runs the Great Backyard Bird Count, in which participants submit data to produce a real-time snapshot of bird populations across North America. Any time of the year, birdwatchers can submit lists of the birds they see on eBird, a huge database of sightings that informs public policy, conservation efforts, and other initiatives.

6. Photograph plants for climate change research.

The Appalachian Mountain Club's Mountain Watch program asks hikers to document alpine and forest plants for ecological research. By taking photos of flowers and fruiting plants along woodland trails and uploading them to the iNaturalist app, participants provide data about the times and places that plants bloom. Scientists then compile the information in an online database and analyze it for trends that could indicate changing climates.

7. Comb through ships' logbooks for weather data.

Old handwritten letters
Practice your handwriting-deciphering skills on the Old Weather project.
scisettialfio/iStock via Getty Images

Ships’ logs from mid-19th century American sailing vessels contain detailed weather observations. Citizen scientists can help transcribe observations from whaling vessels for the Old Weather project; scientists will use the information to learn more about past environmental conditions and create better climate models for future projections. Historians will also use the data to track past ship movements and tell the stories of the people on board.

8. Make American history documents and science notes accessible to more people.

The Smithsonian Libraries are stuffed with original history and science documents that have lain in drawers for decades. Help open up "America's attic" to the public by organizing and transcribing digital versions of handwritten field notebooks, diaries, logbooks, specimen labels, photo albums, and other materials. You'll join thousands of other volunteers to investigate documents like the Sally K. Ride Papers, the collection of the Freedmen's Bureau (which helped former slaves following the Civil War), and field studies of insects by the Irish naturalist Arthur Stelfox.

9. Investigate historical crimes in Australia.

Drawing of a convict ship to Australia
A drawing of a 19th-century convict ship destined for Australia.
Photos.com/iStock via Getty Images

If you're obsessed with true crime, you'll love this project. Volunteer to investigate and transcribe criminal records from 19th- and 20th-century Australia, which was founded as a British penal colony. Alana Piper, a postdoctoral research fellow at the Australian Centre for Public History at the University of Technology Sydney, will use the transcriptions to construct the "life histories and offending patterns of Australian criminals" from the 1850s to the 1940s. More than 40,000 subjects have been completed so far.

10. Map the unique features of Mars's South Pole.

Travel to Mars—without the hassle of zero gravity or space-vegetable farming—through Planet Four, a citizen science project that is currently tasked with identifying features on Mars's dynamic South Pole. Volunteers examine photos from the HiRISE camera on NASA's Mars Reconaissance Orbiter and pick out "fans" or "blotches" in the landscape of seasonal carbon dioxide ice. Scientists believe these structures indicate wind speed and direction on the Martian surface and offers clues about the evolution of the Red Planet's climate.

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