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[Video Link] This is a good six-minute video that explains how transistors work. I liked the description of N- and P-type doping. (Via Adafruit)

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Original author: 
John Timmer

FirasMT

In the past few years, there have been a regular series of announcements about devices that cloak something in space. These typically bend light around the cloak so that it comes out behind the object looking as if it had never shifted at all. In contrast, there's just been a single description of a temporal cloaking device, something that hides an event in time. The device works because in some media different frequencies of light move at different speeds. With the right combination of frequency shifts, it's possible to create and then re-seal a break in a light beam.

But that particular cloak could only create breaks in the light beam that lasted picoseconds. Basically, you couldn't hide all that much using it. Now, researchers have taken the same general approach and used it to hide signals in a beam of light sent through an optical fiber. When the cloak is in operation, the signals largely disappear. In this case the cloak can hide nearly half of the total bandwidth of the light, resulting in a hidden transmission rate of 12.7 Gigabits per second.

The work started with the Talbot effect in mind, in which a diffraction grating causes repeated images of the grating to appear at set distances away from it. The cloaking device relies on the converse of this. At other distances, the light intensity drops to zero. The key trick is to convert the Talbot effect from something that happens in space to something that happens in time.

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Original author: 
timothy

cylonlover writes "A team of scientists at Nanyang Technological University (NTU) in Singapore has developed a new image sensor from graphene that promises to improve the quality of images captured in low light conditions. In tests, it has proved to be 1,000 times more sensitive to light than existing complementary metal-oxide-semiconductor (CMOS) or charge-coupled device (CCD) camera sensors in addition to operating at much lower voltages, consequently using 10 times less energy."

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Original author: 
The Physicist

Physicist: Political conversations with family, for one.

“Friction” is a blanket term to cover all of the wide variety of effects that make it difficult for one surface to slide past another.

There a some chemical bonds (glue is an extreme example), there are electrical effects (like van der waals), and then there are effects from simple physical barriers.  A pair of rough surfaces will have more friction than a pair of smooth surfaces, because the “peaks” of one surface can fall into the “valleys” of the other, meaning that to keep moving either something needs to break, or the surfaces would need to push apart briefly.

This can be used in hand-wavy arguments for why friction is proportional to the normal force pressing surfaces together.  It’s not terribly intuitive why, but it turns out that the minimum amount of force, Ff, needed to push surfaces past each other (needed to overcome the “friction force”) is proportional to the force, N, pressing those surfaces together.  In fact this is how the coefficient of friction, μ, is defined: Ff = μN.

Friction

The force required to push this bump “up hill” is proportional to the normal force.  This is more or less the justification behind where the friction equation comes from.

The rougher the surfaces the more often “hills” will have to push over each other, and the steeper those hills will be.  For most practical purposes friction is caused by the physical roughness of the surfaces involved.  However, even if you make a surface perfectly smooth there’s still some friction.  If that weren’t the case, then very smooth things would feel kinda oily (some do actually).

Sheets of glass tend to be very nearly perfectly smooth (down to the level of molecules), and most of the friction to be found with glass comes from the subtle electrostatic properties of the glass and the surface that’s in contact with it.  But why is that friction force also proportional to the normal force?  Well… everything’s approximately linear over small enough forces/distances/times.  That’s how physics is done!

That may sound like an excuse, but that’s only because it is.

Q: It intuitively feels like the friction force should be directly proportional to the surface area between materials, yet this is never considered in any practical analysis or application.  What’s going on here?

A: The total lack of consideration of surface area is an artifact of the way friction is usually considered.  Greater surface area does mean greater friction, but it also means that the normal force is more spread out, and less force is going through any particular region of the surface.  These effects happen to balance out.

If you have one pillar

If you have one pillar the total friction is μN. If you have two pillars each supports half of the weight, and thus exert half the normal force, so the total friction is μN/2 + μN/2 = μN.

Pillars are just a cute way of talking about surface area in a controlled way.  The same argument applies to surfaces in general.

Q: If polishing surfaces decreases friction, then why does polishing metal surfaces make them fuse together?

A: Polishing two metal surfaces until they can fuse has to do with giving them both more opportunities to fuse (more of their surfaces can directly contact each other without “peaks and valleys” to deal with), and polishing also helps remove impurities and oxidized material.  For example, if you want to weld two old pieces of iron together you need to get all of the rust off first.  Pure iron can be welded together, but iron oxide (rust) can’t.  Gold is an extreme example of this.  Cleaned and polished gold doesn’t even need to be heated, you can just slap two pieces together and they’ll fuse together.

Inertia welders also need smooth surfaces so that the friction from point to point will be constant (you really don’t want anything to catch suddenly, or everyone nearby is in trouble).  This isn’t important to the question; it’s just that inertia welders are awesome.

Q: Why does friction convert kinetic energy into heat?

A: The very short answer is “entropy”.  Friction involves, at the lowest level, a bunch of atoms interacting and bumping into each other.  Unless that bumping somehow perfectly reverses itself, then one atom will bump into the next, which will bump into the next, which will bump into the next, etc.

And that’s essentially what heat is.  So the movement of one surface over another causes the atoms in each to get knocked about jiggle.  That loss of energy to heat is what causes the surfaces to slow down and stop.

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Original author: 
The Physicist

Physicist: Generally speaking, by the time a gas is hot enough to be seen, it’s a plasma.

The big difference between regular gas and plasma is that in a plasma a fair fraction of the atoms are ionized.  That is, the gas is so hot, and the atoms are slamming around so hard, that some of the electrons are given enough energy to (temporarily) escape their host atoms.  The most important effect of this is that a plasma gains some electrical properties that a non-ionized gas doesn’t have; it becomes conductive and it responds to electrical and magnetic fields.  In fact, this is a great test for whether or not something is a plasma.

For example, our Sun (or any star) is a miasma of incandescent plasma.  One way to see this is to notice that the solar flares that leap from its surface are directed along the Sun’s (generally twisted up and spotty) magnetic fields.

A solar flare as seen in the x-ray spectrum.

A solar flare as seen in the x-ray spectrum.  The material of the flare, being a plasma, is affected and directed by the Sun’s magnetic field.  Normally this brings it back into the surface (which is for the best).

We also see the conductance of plasma in “toys” like a Jacob’s Ladder.  Spark gaps have the weird property that the higher the current, the more ionized the air in the gap, and the lower the resistance (more plasma = more conductive).  There are even scary machines built using this principle.  Basically, in order for a material to be conductive there need to be charges in it that are free to move around.  In metals those charges are shared by atoms; electrons can move from one atom to the next.  But in a plasma the material itself is free charges.  Conductive almost by definition.

Jacob's Ladder; for children of all ages

A Jacob’s Ladder.  The electricity has an easier time flowing through the long thread of highly-conductive plasma than it does flowing through the tiny gap of poorly-conducting air.

As it happens, fire passes all these tests with flying colors.  Fire is a genuine plasma.  Maybe not the best plasma, or the most ionized plasma, but it does alright.

Because the flame has a bunch of free charged particles it is pushed and pulled by

The free charges inside of the flame are pushed and pulled by the electric field between these plates, and as those charged particles move they drag the rest of the flame with them.

Even small and relatively cool fires, like candle flames, respond strongly to electric fields and are even pretty conductive.  There’s a beautiful video here that demonstrates this a lot better than this post does.

The candle picture is from here, and the Jacob’s ladder picture is from here.

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Original author: 
Carl Franzen

Quantum-smartcard-qkard-los-alamos_large

It's not quite a quantum internet — yet. But researchers at Los Alamos National Laboratory in New Mexico have developed a new, ultra-secure computer network that is capable of transmitting data that has been encrypted by quantum physics, including video files. The network, which currently consists of a main server and three client machines, has been running continuously in Los Alamos for the past two and a half years, the researchers reported in a paper released earlier this month. During that time, they have also successfully tested sending critical information used by power companies on the status of the electrical grid. Eventually they hope to use it to test offline quantum communication capabilities on smartphones and tablets.

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Original author: 
Germain Lussier

Raid 71 - 2001 A Space Odyssey

Glow in the dark inks on a poster can be hit or miss. In the best cases, they act as almost a night light, revealing a beautiful second image that’s invisible in the day time. On the other hand, some are so subtle and light, it’s almost as if they don’t glow in the dark at all. And maybe that’s a good thing.

The Bottleneck Gallery in Brooklyn, NY will surely have a little of both in their latest exhibit, When The Lights Go Out, which opens April 12. Over 60 artists have made brand new pieces with glow in the dark inks, which will be displayed at all hours via a new installation of blacklights.

Some of the topics of the art include 2001: A Space Odyssey (above), The Shawshank Redemption, Alien, Game of Thrones, Band of Brothers, Where the Wild Things Are, Tron, Poltergeist, Time Bandits and more. It looks like a very fun show. Check out a selection of art below.

When the Lights Go Out opens at 7 p.m. April 12 and will remain open through May 1. It’s located at 60 Broadway, Brooklyn. Find more information at www.bottleneckgallery.com, and that’s also where the show will go on sale online at noon EST on April 13 at that link.

Mouse over each piece for the artist name, and property. Where we can, we’ve placed the original with the glow in the dark element side by side. Some of the images provided either only had one way, or both together. Those are at the bottom of the gallery.

Bruce Yan  - Wild Things
Bruce Yan - Wild Things - GID
Dave Perillo - Time Bandits
Dave Perillo - Time Bandits - GID
Cuyler Smith - Poltergeist
Cuyler Smith - Poltergeist - GID
JP Valderrama - Shawshank
JP Valderrama - Shawshank - GID
Godmachine - Alien - GID
Godmachine - Alien
Rob Loukotka - Band of Brothers - GID
Rob Loukotka - Band of Brothers
Mark Englert - Game of Thrones - GID
Mark Englert - Game of Thrones
Craig Drake - Tron
Raid 71 - 2001 A Space Odyssey

And that’s just a small, small sampling of the full show.

Which is your favorite?

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Original author: 
Carl Franzen

Quantum-key-distribution-airplane_large

In a boost to future secret agents and a blow to their would-be eavesdroppers, German researchers report sending the first successful quantum communications from a moving source — an airplane traveling 180 miles-per-hour — to a stationary receiver on the ground. The study was first performed in 2012 but the results were just made public over the weekend in the journal Nature Photonics.

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