* Posts by Stuart Levy

4 posts • joined 21 Aug 2007

Boffin seeks US Blu-ray, mobile phone import ban

Stuart Levy
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If you doubt that the patent's substantive, go read it!

Thanks, Juillen, for bringing light to this discussion. Wish others had worked harder on doing likewise.

This is no one-click-shopping patent, but a description of a specific family of solutions to a real tech problem. Remember: although red LEDs and lasers have been around a long time, viable blue ones are much newer, because it was hard to make them work.

The patent is quite well written -- not stuffed with obfuscatory language, it actually explains the problem (that among available wide-band-gap materials, always either the n-doped or p-doped version had high resistivity, so you couldn't drive current through them efficiently). It summarizes previous unsatisfactory approaches, and explains briefly but pretty clearly why her scheme works and the processing steps needed to duplicate it.

It also shows how her work fits into the context of related approaches, complete with literature references. It reads kinda like a nice short review paper.

*This* kind of thing is what patents *are* good for.

Oh yeah. If Juillen's post didn't make it easy enough, you can find the patent at:



Iran fires rocket 'into space', plans satellite for '09

Stuart Levy
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Thanks for getting the Ahmadinejad vs. Israel quote right!

Thank you, Mr. Page, for finally getting the Ahmadinejad quote right. Far too many (certainly in the US press) have misquoted him as calling for the *destruction* of Israel, with the implication that that was what Iran intended to do. But that's *not* what Ahmadinejad said!

The effect was much like Krushchev's "We will bury you", which got whipped into being taken as intent to attack the US. But that's not what the Russian phrase meant at all. It was more like "see you at your funeral" -- i.e., we will outlive you, History is on our side, etc. Might well express contempt, but contempt is not aggressive war.


Uranus strikes a pose for Hubble's camera

Stuart Levy

894 years -> 84

Thanks for covering this kind of thing.

Just wanted to note that the "only twice in 894 years" comment must be a typo -- Uranus' orbital period is about 84 years. (So we must see its rings edge-on, if we know to look for them, about every 42 years. Neat.)


Streaking star leaves sweeping tail in its wake

Stuart Levy

space velocities, dwarf vs. giant stars, and GALEX Mira visualization

Re "Sheepspeed reference point" -- there are several common reference frames for measuring space velocities of nearby stars:

(a) relative to our Sun's motion

(b) relative to the "Local Standard of Rest" (google that), the motion of a circular orbit in the Milky Way plane that has the same radius as our Sun's orbit

(a) comes directly from measured quantities: the star's radial velocity, its apparent motion across the sky, and distance. But when I do that I get about 160 km/sec for Mira, so the NASA article's 130 km/sec might be relative to the LSR. Reporting a velocity relative to the Galactic center is certainly possible, but inconvenient -- the star is close to us and far from it -- so an astronomer wouldn't likely do it that way.

130 (or 160) km/sec is pretty fast as nearby stars go. 30-40 km/sec is more typical. (1 km/sec is just about 1 parsec/million years.) So Mira is on an unusual orbit -- most stars stay pretty close to the Milky Way plane, but Mira's orbit must carry it far above and below the plane. It's heading for galactic south at over 100 km/sec.

Re dwarf vs. giant stars, note that a "dwarf" star is just one that's still fusing hydrogen in its core, regardless of whether it's luminous or not, while a "giant" has run out of hydrogen there and is approaching the end of its life (and is generally brighter than it was as a dwarf).

Mira used to be a dwarf star like our sun -- and it's not all that different from how our sun will look in a few billion years. It's a *little* more massive (about 1.2 solar masses, says a recently-updated Wikipedia page). (It has a companion star in orbit around it, so a credible mass estimate is possible.)

At the ends of their lives, when they've run out of hydrogen in their cores, sun-sized stars swell up and go through several giant phases -- Mira is now an "asymptotic giant branch" (AGB) star, a late-phase giant. It's now very swollen, something larger than Mars' orbit, and losing its atmosphere at a great rate.

Rigel and Deneb are also giants -- their core hydrogen has been used up -- but are much more massive than our Sun, so (a) they're 'way more luminous (and were 'way more luminous back when they were dwarf stars too) and (b) their giant phases will end differently -- they'll become supernovae, while stars like Mira and the Sun won't.

Finally, dig this: For the GALEX web site (the satellite that made the observation of Mira's wake), Robert Hurt of Caltech made this lovely artist's-concept animation of how a wake like this might form: