Undisclosed Location

Big storm. Tree down where I originally parked last evening, but I moved my car into better shade. Power out. Fire alarm (luckily false, because the fire department too a long time to show). Hot. Eventually, too hot.

Fled the state in search of an internet connection and juice, yes, the precious juice. Hoping things have been restored by this evening. Enjoy your leap second tonight.

Handy, but Not Deep Thoughts

A few weeks ago Doug Natelson had a post about handy numbers to know … if you’re doing some kind of physics involving liquid nitrogen or liquid helium, or anything else in which a condensed-matter/nanoscale physicists might be involved. (I assume this is in addition to knowing basic constants)

But I do atomic physics. A few favorite things that help me out if I’m away from a calculator or reference book, with some additions from my colleagues. I probably knew more of these, once upon a time.

— The speed of light can be written as 30 GHz-cm. Thus a 30 GHz signal has a wavelength of 1 cm. 1 Ghz means 30 cm.

— 1 nanosecond is 1 foot (light travel in a vacuum)

— a 1 eV photon is 1240 nm

— Room temperature is 1/40 eV (kT)

— Planck’s constant is 0.4 amu-micron-meters/second (useful for deBroglie wavelength calculations)

— There are about $latexpi$  x 10^7 seconds in a year


General reference:

– \(sqrt{g} = pi \) (to about 0.3%) Handy for Pendulum problems — just cancel or combine the two values.

I Love it When a Plan Comes Together

Ancient text gives clue to mysterious radiation spike

An eerie “red crucifix” seen in Britain’s evening sky in ad 774 may be a previously unrecognized supernova explosion — and could explain a mysterious spike in carbon-14 levels in that year’s growth rings in Japanese cedar trees. The link is suggested today in a Nature Correspondence by a US undergraduate student with a broad interdisciplinary background and a curious mind.

Putting the Right Spin on It

Infinite-capacity wireless vortex beams carry 2.5 terabits per second

Actually, it’s not spin. It’s the other angular momentum, pork the orbital variety.

These twisted signals use orbital angular momentum (OAM) to cram much more data into a single stream. In current state-of-the-art transmission protocols (WiFi, LTE, COFDM), we only modulate the spin angular momentum (SAM) of radio waves, not the OAM. If you picture the Earth, SAM is our planet spinning on its axis, while OAM is our movement around the Sun. Basically, the breakthrough here is that researchers have created a wireless network protocol that uses both OAM and SAM.

I couldn’t get a mental image of how you’d do this, but I think that’s because I was thinking about individual photons, and I don’t see how to get a photonic orbital angular momentum state. But this is data transmission, which can be analog, or even of it’s digital a “one” is made up of a bunch of photons, i.e. it’s classical.

So I grabbed the paper I could (an earlier one that demonstrated the effect, and to which I had access). Here’s what the antenna looks like

The light being sent will have a different phase depending on what part of the antenna is transmitting it, which gives you the vortex. 3 GHz signals have a wavelength of 10 cm, so that’s probably gives you the scale of the depth of the slice in the parabolic dish.

This technique is likely to be used in the next few years to vastly increase the throughput of both wireless and fiber-optic networks.

I think this is overly optimistic. It’s going to take time to make this robust for data transmission and then you have to deploy the technology. And fiber-optics? I don’t see how this would work in a fiber (a less forgiving environment to good polarization, which is likely to cause problems here), but I also don’t see it as being necessary. I don’t think fiber is as clogged as the RF spectrum is, and you can always add more fiber if you need to.

This Just In: Bearing False Witness No Longer a Sin

Apparently, anyway.

How American fundamentalist schools are using Nessie to disprove evolution

Jonny Scaramanga, 27, who went through the ACE programme as a child, but now campaigns against Christian fundamentalism, said the Nessie claim was presented as “evidence that evolution couldn’t have happened. The reason for that is they’re saying if Noah’s flood only happened 4000 years ago, which they believe literally happened, then possibly a sea monster survived.

“If it was millions of years ago then that would be ridiculous. That’s their logic. It’s a common thing among creationists to believe in sea monsters.”

Private religious schools, including the Eternity Christian Academy in Westlake, Louisiana, which follows the ACE curriculum, have already been cleared to receive the state voucher money transferred from public school funding, thanks to a bill pushed through by state Governor Bobby Jindal.

A Taste of Honey

A Beekeeper’s Perspective on Risk

Here’s another lesson by analogy: No queen bee is under pressure for quarterly pollen and nectar targets. The hive is only beholden to the long term. Indeed, beehives appear to underperform at times because they could collect more. But they are not designed to maximize current returns; they are designed to prevent cycles of feast and famine (a death sentence in the natural world). They concentrate their foraging on the most lucrative patches but keep an exploratory force in the field that will ensure future revenue sources when the current ones run dry. This exploratory force (call it an R&D expenditure) increases as conditions worsen.

Interesting perspective. Quite the opposite of what many businesses are doing these days.