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Researchers at Duke Are Perfecting an Invisibility Cloak

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Duke University researchers perfect the illusion of invisibility using a new light-bending method.

Over the past few years, the science world has produced no shortage of invisibility cloaks. But unlike the magical, fictional kind donned by Harry Potter and Co., these shimmery offerings were less than perfect: While most could bend light around an object, they all reflected some of what's called incident light, compromising the illusion's success. Now for the first time, researchers from Duke University have created a "flawless" invisibility cloak capable of disguising tiny objects, in this case a 7.5 by 1 cm cylinder.

Invisibility cloaks typically work by bending electromagnetic waves — like visible light — around a three-dimensional object. Rather than seeing that object, onlookers instead catch a glimpse of what's directly behind it. Scientists are able to achieve this illusion using something called metamaterials, or man-made objects that never occur in nature but can bend electromagnetic waves in all sorts of weird ways.

However, the degree to which these metamaterials can bend something like light is limited. Sebastian Anthony at ExtremeTech explains:

"Metamaterials get you most of the way, but they still need to be arranged in such a way that the illusion is perfect. To get around a 3D object, you have to turn a corner at some point — and previous cloaks have struggled to fashion metamaterials that bend waves around corners without causing reflections, which ruin the illusion."

In this case, Duke University researchers came up with a so-called "perfect arrangement": Position the metamaterials in a diamond pattern that eliminates reflective light entirely. In this experiment, they were able to hide the miniature cylinder completely from a different kind of electromagnetic wave, but one whose properties still translate, at least in theory, to visible light — microwaves.

The diamond arrangement has its limitations, however: It only works in one direction. "It's like the card people in Alice in Wonderland," Prof. David Smith, a Duke researcher who worked on the project, tells BBC News. "If they turn on their sides you can't see them but they're obviously visible if you look from the other direction."

But the design principle is a big step forward in the quest to prove that total invisibility is indeed possible. In the near future researchers hope to apply their findings to an omnidirectional cloak that can hide an object no matter where an observer is situated.

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
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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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iStock
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Why Your iPhone Doesn't Always Show You the 'Decline Call' Button
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iStock

When you get an incoming call to your iPhone, the options that light up your screen aren't always the same. Sometimes you have the option to decline a call, and sometimes you only see a slider that allows you to answer, without an option to send the caller straight to voicemail. Why the difference?

A while back, Business Insider tracked down the answer to this conundrum of modern communication, and the answer turns out to be fairly simple.

If you get a call while your phone is locked, you’ll see the "slide to answer" button. In order to decline the call, you have to double-tap the power button on the top of the phone.

If your phone is unlocked, however, the screen that appears during an incoming call is different. You’ll see the two buttons, "accept" or "decline."

Either way, you get the options to set a reminder to call that person back or to immediately send them a text message. ("Dad, stop calling me at work, it’s 9 a.m.!")

[h/t Business Insider]

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