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After Losing a Limb, Jellyfish Reorganize Their Bodies for Symmetry

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After losing a limb, some animals, such as lizards and salamanders, can regenerate the missing body part. Jellyfish deal with amputation in a different way: They simply rearrange their bodies to compensate for the limb they lost. This unique strategy involves reorganizing existing body parts to reestablish symmetry, a group of researchers from the California Institute of Technology report in PNAS

From left to right, the process of symmetrization, starting with the amputated state. Image Credit:Michael Abrams, Ty Basinger, and Christopher Frick, California Institute of Technology

After anesthetizing moon jellies in the lab, researchers amputated multiple limbs to see how they would regain symmetry, which is essential for their ability to move through the water. The jellyfish did so by rearranging their remaining arms and muscles, and moving their mouths to the new center of their bodies. 

The process commenced within minutes,” the researchers write. “The wound at the cut site closed within the first hours. The arms gradually spread further apart, as the manubrium [the jellyfish equivalent of a throat] relocated to the center of the body.” The jellyfish typically regained their bodily symmetry within 12 hours, whether they were placed in light or dark conditions, upside down, in groups or alone. 

To shed light on the process behind these contortions, the scientists next put muscle relaxants in the water with the jellyfish. By preventing the jellyfish's muscles from contracting, they succeeded in stopping the symmetrization process, suggesting that the action of healing after an injury is triggered by movement.

The way jellies move through the water—alternating powerful propulsive muscle contractions with more elastic movement of their jelly-like bodies—may steadily move the remaining body parts into position. “This is akin to squeezing an elastic ball at one end and producing a protrusion on the other side,” the researchers postulate. “With each cycle of compression and elastic repulsion, the arms may then relax to a new stable state.”

The true lesson here: don't try to hack a jellyfish to pieces, because they will come back to haunt you. 

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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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May 23, 2017
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