Archive for June, 2009

Energy Balance

Food, energy outpace production

By 2050, world population is expected to exceed 9 billion people, up from 6.5 billion today. Already, according to the report, a gap is emerging between agricultural production and demand, and the disconnect is expected to be amplified by climate change, increasing demand for biofuels, and a growing scarcity of water.

(S)Poof!

Another video, reminiscent of the viral popcorn-popped-with-a-cellphone video I discussed a while back

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And, in fact one of the response videos is with popcorn

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Also one involving toast

Objections: One is electrostatic. Matt has been discussing static charge distributions recently (here and here) and it’s very important to note that he’s discussing charge distributions on conductors — the charges can easily rearrange themselves. But in these video examples, the people and the targets are not conductors. So while you might build up some static charge on a person (in a very questionable display of boys gleefully rubbing other boys with balloons. Not that there’s anything wrong with that, if that’s who you are, balloon-fetish-freaks). A discharge to another insulator just isn’t going to send the energy where you want it to. A small discharge will even out the potential difference, and you’re done. A full discharge needs to be to a conductor, preferably a grounded one.

Speaking of sending the energy, how much energy are we discussing here? I’m not sure how much energy it takes for an eggsplosion, but I’m guessing we’re talking well above a few Joules. Accounting for my slight overestimation of the water content in the earlier popcorn analysis, it probably still takes somewhere north of 10 Joules of energy to pop a single kernel. Can we get anywhere close with static charge?

The energy stored in a capacitor is 1/2 CV^2. The capacitance of the human body is a few hundred picofarads. Let’s be generous and say it’s 2,000 picofarads (pico is 10^-12). How much of a potential difference do we need for 10 Joules? Do the math — it’s 100 kV. A few kV makes for a painful spark when discharging to a doorknob. A 5 mm spark between conducting spheres happens at about 16 kV. A realistic spark leaves us at significantly less than a Joule of energy.

Spoof

Stalking the (Wild) Physicist

Via Fine Structure, The World’s Greatest Physicists (as Determined by the Wisdom of Crowds)

Mikhail Simkin and Vwani Roychowdhury at the University of California, Los Angeles, have come up with a way of ranking physicists by equating their achievements with their fame as measured by hits on Google.

Duking it Out

Nuke ’em

Ground Zero II

Have you ever wondered what would happen if a nuclear bomb goes off in your city? With Google’s Maps framework and a bit of Javascript, you can see the outcome. And it doesn’t look good.

Vintage Lab Pictures

I was decreasing the local entropy in a small part of my abode and found a shoebox full of photos which happened to contain a few shots of my grad school lab, in all its glory. We were building an interferometer which would use cold atoms, which means relatively large deBroglie wavelengths and a correspondingly small system. But one has to trap the atoms and cool them down first, and then generate the cold beam of atoms to feed into the diffraction gratings that comprise the interferometer, so the system is still quite complex. Since I was the first PhD candidate in the group, it meant I was involved in the construction of most of the components of the lab apparatus pictured here. It also meant a lot of fumbling in the dark, both figuratively and literally, since the only one with any experience with doing this kind of work was the PI, who had other duties (like teaching, writing grant proposals, etc.) It was a big day when the group finally reached the point where we didn’t want him playing with the experiment, because we knew more about the details than he did. That took a couple of years.

Here’s the vacuum system.

osu-vacuum-system

At the bottom of the picture is the oven, which was basically a pipe bomb with a hole in it (under vacuum, of course), and when heated sufficiently, would spray Rubidium atoms out. These were collimated with a second hole a few cm away (the extra Rb was collected on some cold metal and sent back into the oven during a refill cycle we ran each night after running the oven). Underneath is a turbo pump and a roughing pump; the small green hose was for adding dry nitrogen if we needed to open the system up. The nitrogen was supposed to keep the Rb from reacting with water in the air. It never worked.

The long pipe leads down to the next part of the vacuum system, and it has a “wobble stick” that blocks the atomic beam, if desired, and a valve to isolate the two parts of the system. You can also see an ion gauge on the left which was normally off so the light from the filament wouldn’t register on any photodiodes or the photomultiplier tube.

The tube is about a meter or so long, and needed to be so we could slow the atoms down. A laser was sent down the tube from the other end, and “chirped” in frequency to account for the changing Doppler shift — you wanted the laser to track the resonance of the atoms as they slowed down, so they would keep scattering photons. Once the atoms were slow enough, the laser turned off, and the atoms drifted into the bigger chamber, where they were trapped in a two-dimensional trap called an “atomic funnel.” They were able to move along the axis of the funnel, and were forced out to the left into the region where the interferometer would be. I made the gratings for the interferometer, but never got to the point where the apparatus was finished.

Here is an early version of the funnel:

old-hairpin

It’s a “hairpin” made of copper tubing so we could water-cool it while sending several amps through it, and it creates a quadrupole field in two dimensions, so that atoms would be trapped into a pencil shape along the central axis, left-to-right. It’s supported from below by two insulated standoffs — you can see the ceramic, i.e. insulating, part — to keep it straight. The dark hole straight through it is the tube leading to the oven and the lighter window on the left would be where one of the six trapping lasers would come in. Up top there is a tube with some lenses in it for imaging the trap, and on the right is a target for aligning the lasers. The target is on a linear feedthrough, and the target could be inserted into the center and all of the lasers sent through it to make sure they all overlapped where they should.

The funnel tubes were originally soldered together. What you see here is version 2, because at one point we lost cooling water while the system was energized, and the solder melted. Which meant that lots of water was introduced to the system and it became a giant fish tank, sans fish. Fortunately, we had interlocks in the system so that if the pressure rose too high the pneumatic valves would shut (that’s what the rest of the green tubing is for in the first picture), and the damage was limited. The white blobs at the ends of the little elbows are torr-seal, which we used to repair the trap. This eventually failed, too, and we replaced it with a much better trap fashioned from a single piece of copper tubing.

new-hairpin

I graduated after having built much of this and characterizing the atomic beam. We were able to extract atoms going up to 10 m/s — this was adjustable, depending on the laser frequencies of the different beams, but atoms going too slow would miss the interferometer because of gravity, so we didn’t bother trying to generate a beam going below a couple of m/s. The atoms were also somewhat cold — less than a milliKelvin — so that the beam didn’t spread out too much. At the time, one other funnel had been built, but it had on of its lasers along the axis of the funnel, which precluded putting any sort of target there. This was novel enough for a publication (T. B. Swanson, N. J. Silva, S. K. Mayer, J. J. Maki, and D. H. McIntyre, “Rubidium atomic funnel,” J. Opt. Soc. Am. B 13, 1833-1836 (1996)) and more importantly, a degree.

Color My World

Cool illusion. Bad Astronomy: The blue and the green

This is why I tell people over and over again: you cannot trust what you see even with your own eyes. Your eyes are not cameras faithfully taking pictures of absolute truth of all that surrounds you. They have filters, and your brain has to interpret the jangled mess it gets fed. Colors are not what they appear, shapes are not what they appear (that zoomed image above is square, believe it or not), objects are not what they appear.

Yeah. Ditto

Doctor Incredible

100 Incredible Lectures from the World’s Top Scientists

Billy Mays Wants You to Know

A Higgs Boson without the Mess

Sounds like a late-nite ad. It’s Higgsy Clean!

A proton is always surrounded by a swarm of ghostly virtual photons and gluons associated with the fields of the electromagnetic and strong nuclear forces. Researchers have predicted that when two protons (or a proton and an antiproton) fly past one another at close range, within about a proton’s diameter, these virtual particle clouds may occasionally interact to create new, real (not virtual) particles. The original protons would merely lose some momentum and separate from the beam. Such an “exclusive” reaction–where the original particles don’t break apart–gives unusually clean data because there are so few particles to detect.

Cuuuut!

“Filming in the lab” is the recent theme at PhD comics, and this one grabs the essence. (Or you can start at the beginning, if you’re one of the type that needs to do that.)

I’ve been filmed in the lab and interviewed on TV once, and I’ve observed my colleagues being filmed and interviewed. There’s a pattern to it. They sit you down in front of one of your impressive-looking pieces of lab apparatus and ask questions for a while. For every 15 minutes of interview, approximately 5 seconds will make it to air time in the final story (my data point, at least). Next, they will want some “action” shots of you, which for an atomic physics/optics lab usually means adjusting some mirrors or twiddling a knob on a piece of electronics and looking at an oscilloscope with a serious expression on your face. If there are two of you in the shot, one of you will need to be pointing at the oscilloscope, as if to say, “Here is where the WOW signal would be, if we had a signal. But we don’t, because we can’t run our experiment with these floodlights on.” Obviously “action shot” here does not the mean same thing as in an episode of some detective series — this is no Magnum, Principle Investigator. A third component that is sometimes used is of one of the interviewee walking down a corridor or sidewalk, so that the reporter can do a voice-over. Alternately they will just get shots of the equipment, especially if it whirs and moves about, for that segment.

Then they mash it all together and if you’re lucky they won’t have gotten the science horribly wrong.

Commutation Relations

[finger, prick] ≠ 0

( … lots of George Carlin on HBO lately … )

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