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Engineers Design Device to Listen to Knees’ Snaps, Crackles, and Pops

We tend to associate creaking, popping joints with old age, but your joints make tiny little noises every time you move, no matter your age. These noises are so faint, we usually can’t hear them with the naked ear. But one team of engineers at the Georgia Institute of Technology (GIT) wants to listen in on the noises made by joints, and they built a device that lets them do just that. The team shared a report of their progress in the online journal IEEE Transactions on Biomedical Engineering.

The project started with a call for research proposals on rehabilitation technology from the Defense Advanced Research Projects Agency (DARPA). The military has a lot of motivation to advance rehab technology. From basic training to deployment, soldiers undergo intense physical stresses, whether that’s carrying hundred-pound backpacks, marching for miles and miles, or darting through an active war zone.

"What most people don't know is that musculoskeletal injuries of the knees and ankles are among the top reasons for discharge for active duty service members," GIT engineer and paper co-author Omer Inan said in a press statement.

But like products developed for NASA, technologies created with the military in mind often trickle down to civilians. Inan, for example, is not a career military man, but he was a discus thrower in college and has first-hand (or first-knee) knowledge of the strain athletes put on their joints. Although he retired from sports years ago, Inan can still feel—and hear—the damage in his knees.

He and his colleagues realized that those snapping, crackling, popping noises might be a good indicator of injury. They created a knee band outfitted with microphones and vibration sensors that record sounds in the air and inside the body.

Typical knee-popping sounds are one thing, but the in-body crunching and grinding noises are … well, kind of nauseating. Listen for yourself:

"It's a little bit like some kind of Halloween stuff happening,” Inan said. “You're listening to your bones rubbing on each other, or maybe cartilage."

The in-body noises of both healthy knees and damaged knees sound pretty disgusting, but they do produce different patterns of sound, which could make the knee band a great diagnostic device.

Though progress has been made, the device is not quite ready yet. Getting a clear recording can be hard; our joints are surrounded by fluid, which can dampen sound waves that emanate from the joint. Additionally, the recordings must be taken while a patient is moving, but that movement makes its own noises.

Inan and his colleagues will continue to test and improve their design, and the medical technology world will be listening closely.

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Stones, Bones, and Wrecks
Buckingham Palace Was Built With Jurassic Fossils, Scientists Find
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The UK's Buckingham Palace is a vestige from another era, and not just because it was built in the early 18th century. According to a new study, the limestone used to construct it is filled with the fossilized remains of microbes from the Jurassic period of 200 million years ago, as The Telegraph reports.

The palace is made of oolitic limestone, which consists of individual balls of carbonate sediment called ooids. The material is strong but lightweight, and is found worldwide. Jurassic oolite has been used to construct numerous famous buildings, from those in the British city of Bath to the Empire State Building and the Pentagon.

A new study from Australian National University published in Scientific Reports found that the spherical ooids in Buckingham Palace's walls are made up of layers and layers of mineralized microbes. Inspired by a mathematical model from the 1970s for predicting the growth of brain tumors, the researchers created a model that explains how ooids are created and predicts the factors that limit their ultimate size.

A hand holding a chunk of oolite limestone
Australian National University

They found that the mineralization of the microbes forms the central core of the ooid, and the layers of sediment that gather around that core feed those microbes until the nutrients can no longer reach the core from the outermost layer.

This contrasts with previous research on how ooids form, which hypothesized that they are the result of sediment gathered from rolling on the ocean floor. It also reshapes how we think about the buildings made out of oolitic limestone from this period. Next time you look up at the Empire State Building or Buckingham Palace, thank the ancient microbes.

[h/t The Telegraph]

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Space
10 Astonishing Things You Should Know About the Milky Way
Anne Dirkse, Flickr // CC BY-SA 2.0
Anne Dirkse, Flickr // CC BY-SA 2.0

Our little star and the tiny planets that circle it are part of a galaxy called the Milky Way. Its name comes from the Greek galaxias kyklos ("milky circle") and Latin via lactea ("milky road"). Find a remote area in a national park, miles from the nearest street light, and you'll see exactly why the name makes sense and what all the fuss is about. Above is not a sky of black, but a luminous sea of whites, blues, greens, and tans. Here are a few things you might not know about our spiraling home in the universe.

1. THE MILKY WAY IS GIGANTIC.

The Milky Way galaxy is about 1,000,000,000,000,000,000 kilometers (about 621,371,000,000,000,000 miles) across. Even traveling at the speed of light, it would still take you well over 100,000 years to go from one end of the galaxy to the other. So it's big. Not quite as big as space itself, which is "vastly, hugely, mind-bogglingly big," as Douglas Adams wrote, but respectably large. And that's just one galaxy. Consider how many galaxies there are in the universe: One recent estimate says 2 trillion.

2. IT'S JAM-PACKED WITH CELESTIAL STUFF.

artist's illustration of the milky way galaxy and its center
An artist's concept of the Milky Way and the supermassive black hole Sagittarius A* at its core.
ESA–C. Carreau

The Milky Way is a barred spiral galaxy composed of an estimated 300 billion stars, along with dust, gas, and celestial phenomena such as nebulae, all of which orbits around a hub of sorts called the Galactic Center, with a supermassive black hole called Sagittarius A* (pronounced "A-star") at its core. The bar refers to the characteristic arrangement of stars at the interior of the galaxy, with interstellar gas essentially being channeled inward to feed an interstellar nursery. There are four spiral arms of the galaxy, with the Sun residing on the inner part of a minor arm called Orion. We're located in the boondocks of the Milky Way, but that is OK. There is definitely life here, but everywhere else is a question mark. For all we know, this might be the galactic Paris.

3. FOR A SPIRAL GALAXY, IT'S PRETTY TYPICAL …

If you looked at all the spiral galaxies in the local volume of the universe, the Milky Way wouldn't stand out as being much different than any other. "As galaxies go, the Milky Way is pretty ordinary for its type," Steve Majewski, a professor of astronomy at the University of Virginia and the principal investigator on the Apache Point Observatory Galactic Evolution Experiment (APOGEE), tells Mental Floss. "It's got a pretty regular form. It's got its usual complement of star clusters around it. It's got a supermassive black hole in the center, which most galaxies seem to indicate they have. From that point of view, the Milky Way is a pretty run-of-the-mill spiral galaxy."

4. …AND YET IT STANDS OUT AMONG ALL GALAXIES.

On the other hand, he tells Mental Floss, spiral galaxies in general tend to be larger than most other types of galaxies. "If you did a census of all the galaxies in the universe, the Milky Way would seem rather unusual because it is very big, our type being one of the biggest kinds of galaxies that there are in the universe." From a human perspective, the most important thing about the Milky Way is that it definitely managed to produce life. If they exist, the creatures in Andromeda, the galaxy next door (see #9), probably feel the same way about their own.

5. FIGURING OUT ITS STRUCTURE FROM THE INSIDE IS A CHALLENGE.


John McSporran, Flickr // CC BY 2.0

We have a very close-up view of the phenomena and forces at work in the Milky Way because we live inside of it, but that internal perspective places astronomers at a disadvantage when it comes to determining a galactic pattern. "We have a nice view of the Andromeda galaxy because we can see the whole thing laid out in front of us," Majewski says. "We don't have that opportunity in the Milky Way."

To figure out its structure, astronomers have to think like band members during a football halftime show. Though spectators in the stands can easily see the letters and shapes being made on the field by the marchers, the band can't see the shapes they are making. Rather, they can only work together in some coordinated way, moving to make these patterns and motions on the field. So it is with telescopes and stars.

6. INTERSTELLAR DUST BLOCKS OUR VIEW OF SOME PARTS OF THE GALAXY.

Interstellar dust further stymies astronomers. "That dust blocks our light, our view of the more distant parts of the Milky Way," Majewski says. "There are areas of the galaxy that are relatively obscured from view because they are behind huge columns of dust that we can't see through in the optical wavelengths that our eyes work in." To ameliorate this problem, astronomers sometimes work in longer wavelengths such as radio or infrared, which lessen the effects of the dust.

7. THE MILKY WAY SPINS, BUT ITS SPEED DOESN'T ADD UP …

Astronomers can make pretty reasonable estimates of the mass of the galaxy by the amount of light they can see. They can count the galaxy's stars and calculate how much those stars should weigh. They can account for all the dust in the galaxy and all of the gas. And when they tally the mass of everything they can see, they find that it is far short of what is needed to account for the gravity that causes the Milky Way to spin.

In short, our Sun is about two-thirds of the way from the center of the galaxy, and astronomers know that it goes around the galaxy at about 144 miles per second. "If you calculate it based on the amount of matter interior to the orbit of the Sun, how fast we should be going around, the number you should get is around 150 or 160 kilometers [93–99 miles] per second," Majewski says. "Further out, the stars are rotating even faster than they should if you just account for what we call luminous matter. Clearly there is some other substance in the Milky Way exerting a gravitational effect. We call it dark matter."

8. … AND WE BLAME DARK MATTER FOR THAT.

Dark matter is a big problem in galactic studies. "In the Milky Way, we study it by looking at the orbits of stars and star clusters and satellite galaxies, and then trying to figure out how much mass do we need interior to the orbit of that thing to get it moving at the speed that we can measure," Majewski says. "And so by doing this kind of analysis for objects at different radii across the galaxy, we actually have a fairly good idea of the distribution of the dark matter in the Milky Way—and yet we still have no idea what the dark matter is."

9. THE MILKY WAY IS ON A COLLISION COURSE WITH ANDROMEDA. BUT DON'T PANIC.

andromeda galaxy
The Andromeda galaxy
ESA/Hubble & NASA

Sometime in the next 4 or 5 billion years, the Milky Way and Andromeda galaxies will smash into each other. The two galaxies are about the same size and have about the same number of stars, but there is no cause for alarm. "Even though there are 300 billion stars in our galaxy and a comparable number, or maybe more, in Andromeda, when they collide together, not a single star is expected to hit another star. The space between stars is that vast," Majewski says.

10. WE'RE THROWING EVERYTHING WE HAVE AT STUDYING IT.

There are countless spacecraft and telescopes studying the Milky Way. Most famous is the Hubble Space Telescope, while other space telescopes such as Chandra, Spitzer, and Kepler are also returning data to help astronomers unlock the mysteries of our swirling patch of stars. The next landmark telescope in development is NASA's James Webb Space Telescope. It should finally launch in 2019. Meanwhile, such ambitious projects as APOGEE are working out the structure and evolution of our spiral home by doing "galactic archaeology." APOGEE is a survey of the Milky Way using spectroscopy, measuring the chemical compositions of hundreds of thousands of stars across the galaxy in great detail. The properties of stars around us are fossil evidence of their formation, which, when combined with their ages, helps astronomers understand the timeline and evolution of the galaxy we call home. 

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