Recently in 2007 Science Category

Arrow of Time

Yesterday, Jess took and ran with my analogy between extreme cold and radiation. (Although I think that entry is locked, so not everyone will be able to see it.) At one point she says, "the Second Law of Thermodynamics, the law of increase of entropy that, in a way, defines the direction of time for the universe...".

This refers to the open question regarding why time appears to flow in one direction only, often called the Arrow of Time Problem. One of my old cosmology profs is now out in California, blogging and thinking about the Arrow of Time. Probably not in that order. But Jess' post reminded me of a recent post of his, an Arrow of Time FAQ.

Published

The trouble with the sort of experimental science that I do is that you tend to go a while between publications. The vast majority of your time being consumed by, for instance, making sure that your telescope doesn't turn right in response to a command to go up. (So far as I know, it doesn't.) This is in marked contrast to my observer friends down the hall, who appear to spend more time trying to corral their results into papers than they do actually obtaining said results. On the third hand, I have no clear idea of how exactly the theorists upstairs spend their days, except that it seems to involve more coffee than the rest of us put together.

Point being, last year I successfully scored another paper, which came out this month. By all means check out the January issue of Applied Optics if you're into that sort of thing. Here's the abstract, with the full PDF text available from there as well.

"Comparison of the crossed and the Gregorian Mizuguchi-Dragone for wide-field millimeter-wave astronomy" by H. Tran, A. Lee, S. Hanany, M. Milligan, and T. Renbarger grew out of some work I was involved in a couple of years back when we were hammering out the optical design for the EBEX telescope. We found that a wide swath of the design space could be collapsed down to a choice between two different classes of telescope geometry, and that the pros and cons of that choice weren't well understood, at least for millimeter-waves. These frequencies roughly straddle the worlds of radio astronomy (where telescopes are designed using well understood principles of antenna physics) and optical astronomy (which relies upon the similarly well understood field of optics). As a result, to really understand the trade-offs, we needed to consider both worlds. Add to that the fact that we're interested in really high-precision polarization measurements, which is considered a rather quirky subfield on its own. Then it's easy to understand how we'd stumbled onto a problem that had barely been considered before, but has become quite important in recent years as the significance to cosmology of the polarization of the CMB has been recognized, and numerous teams have joined the race to observe it.

Burnin' Dark Matter

Yesterday I gave a talk on "Stars Powered by Dark Matter" that I think came out pretty well. The overall gist, after giving a really brief overview of WIMPy dark matter, that stars tend to accumulate dark matter particles in their interiors, and at high enough concentrations this starts to have potentially interesting effects. In particular, WIMPs (i.e. particles of dark matter) probably self-annihilate. That is to say, if you bring two WIMPs together, they will annihilate just like matter and antimatter. However, you have to get them really, really close together for this to happen -- we know this, because otherwise you'd see lots of gamma rays and whatnot from all over due to WIMPs annihilating in the halo of dark matter surrounding our own galaxy.

I considered four cases. First, working mostly off this 2002 paper by Bottino, I discuss the amount of dark matter likely to build up in our own Sun. You get some 1024 or so particles per second, which annihilate to add a few petawatts of energy to the Sun's core. Sounds like a lot, but it's completely negligible to a star, and the effects are too small for us to detect.

Next, Fairbairn et al have a preprint out discussing what happens if you ramp up the dark matter concentration. Turns out, if you make the dark matter particles a billion times more common than we think they are around us (here, we think it's probably several per cubic meter, depending on how massive you think the particles are), the dark matter annihilation produces more energy in the star's core than would nuclear burning, and you get a so-called "WIMP burner". Of couse, finding such a high concentration of dark matter might be tricky...

So I also talked about some work from earlier this year (this conference proceeding and this paper) by Igor Moskalenko and Lawrence Wai. They think you can get such huge concentrations of WIMPs near the supermassive black hole at the center of a galaxy. Apparently, you could have a white dwarf -- a dense, dead, burned-out star -- that swings within a milliparsec of the black hole and captures enough dark matter to put out ten times the luminosity of the sun. That's twice the distance from us to the Voyager probes, but still pretty close when you're talking about a million-solar-mass black hole.

Finally I mentioned this paper by Spolyar et al that suggests that WIMP annihilation could have prevented the first stars from forming right away (or possibly, at all). Instead, they would remain the dense, dark clouds that we normally expect to form protostars, prevented from continuing their collapse because they can't get rid of the dark matter energy fast enough. If this model is right, that's an effect that the folks who study the first stars and their effects are going to have to find a way around.

Observing with Knobs and Gears

Photo post, just because I can!

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Observing with the refractor. This was taken back in November during one of my comet Holmes observing runs.

Algorithms

Earlier this week I was fairly pleased with myself for writing a reasonably elegant piece of code that takes a bunch of variously-sized chunks of data and works out how to efficiently and predictably squeeze them into the spare bandwidth of another data stream.

The next day, I think while walking to the grocery store, it occurred to me that I could do the same thing with a mapping trick and some modular arithmetic.

I was prematurely pleased with myself. That version took two lines of code.

In New York

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So I'm off to the big city (i.e. New York) tomorrow for about a week. I'll mostly be in meetings, but anyone out that way interested in getting together, drop me a line. Once that is over with, this blog will hopefully become more interesting again.

I didn't forget entirely about our friendly local comet-in-outburst, which last time we had clear skies was still visible in the northeast. The picture below, again taken afocally through our 10-inch refractor, shows what it looked like a couple of weeks ago. Now it's expanded so much that it's an obvious fuzzball in the sky, and is really too large to photograph well through a telescope. And anyway, the interesting structures are now too low surface brightness to capture well with my equipment. As it is, to get the outer parts of the coma below, the sensitivity is turned way up, which produces the grainy texture (i.e. noise). As Jess put it, the quantum efficiency of my detector is rather low.

(Sudden flashback! This is what it looked like through the refractor right after the outburst, and this is what our skies looked like soon after.)

People with professional -- pricy -- equipment are, of course, having a field day. For example, over the past couple of weeks deep exposures revealed the comet developing and then releasing an ion tail. On the other hand, if you go to high resolution instead of exposure time, observers are noting all kinds of interesting jet-like structures showing up near the comet nucleus. Interestingly, that later picture was taken by a remote-controllable automated scope that you can apparently rent time with online. Which sort of makes amateur astronomy work the same way as it does for researchers, who these days often get nowhere near the telescopes that produce their observations.

In my research, on the other hand, we actually have to build the telescope before we can fly it. Which might explain why I enjoy cranking up the old refractor and fiddling around until I can take acceptable photos with whatever cheap equipment I have handy. It's just fun.

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Comet 17P/Holmes on 1 November 2007, about a week after the outburst.

Finding the Comet

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Comet 17P/Holmes remains excitingly bright, and the shell of dust from its recent outburst is now large enough to be seen with the unaided eye -- it no longer looks at all like a star.

I took these photos back on Saturday, when the comet was still quite condensed, but as you can see in the upper image, there is distinct fuzziness even in a very low-zoom photo. (The stars appear as short lines because the camera was stationary for this shot, so the sky moved by a few arcminutes, comparable to the width of the comet's coma.)

Below, a wide-angle view of the sky looking northeast an hour or so after sunset. Very lightly processed to de-emphasize the Moonlight flooding the sky (the full Moon was hiding right behind the dome at bottom). Near the center of the image you'll recognize the triangle from the top photo, where the lower left object is the comet. At the very bottom is the brilliant white star Capella -- if you're looking for the comet under city lights, start by finding that. Even in the most light-polluted areas, it should be possible to spot this comet with binoculars (I'm looking at you, readers in New York).

Tonight the Moon doesn't rise for several hours after sunset, so the evening should be quite reasonably dark. Since we've got clear skies here, I plan to take the telescope for another spin, even despite the cold I'm battling.

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Comet Holmes in Perseus as seen from the roof of the Physics Building here. Click either photo for a larger version.

Comet

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Looking down the tubes of our refractor (and its finder scopes), out the slit, past the Moon, at a fuzzball three times as distant as Mars.

No, I haven't abandoned the blog. It's just been a busy, erm ... month.

Anyhow, Comet 17P/Holmes is putting on a show at the moment, what with getting a half-million times brighter in a matter of hours. Now it's about 48 hours later, and sky watchers everywhere are having a ball with it.

Obviously I can't let everybody else have all the fun, and I just so happen to have a century-old 10-inch refractor up on the roof and some history with astrophotography, so here's my contribution. (Click pictures for full-rez versions.)

We estimated the comet was at about magnitude 2.5 at the time, which generally agrees with the reports coming in, and looked to be about an arcminute across. Given that it's about 1.5 AU from us (three times as far away as Mars!) that coma is around 60,000 kilometers wide. If it's around 30 hours post-eruption in the picture below, that dust cloud is expanding at 600 meters per second. Reports indicate that it's expanded considerably tonight.

Conspicuously, there's no tail. For one thing, it'll take some time for the sun to sculpt this expanding cloud; for another, the tail would be pointed almost directly away from us, anyway. It's actually on its way out now, but it only has to get out to the orbit of Jupiter, so 17P isn't going anywhere in a hurry. Whether or not it stays bright, on the other hand, is anyone's guess.

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A closer look at the sky, and then a much closer look through the 10-inch.

Aurigids

Friday night I was out at O'Brien running a Universe in the Park event, and throughout the evening I and the attendees kept noticing a highly unusual number of bright meteors in the sky. Apparently, it wasn't just us:

It was just before dawn and awfully cold in Independence Pass near Aspen, Colorado. Photographer Thomas O'Brien couldn't help falling asleep. Fortunately, his camera kept shooting, recording a beautiful Saturday morning outburst of Aurigid meteors:

"I never saw one myself," he says. Nevertheless, for about 30 minutes around 4:30 PDT (1130 UT) the sky was filled with colorful meteors and fireballs. Sightings have been reported in Arkansas, Arizona, Colorado, California, Idaho, Indiana, Kansas, New Mexico, Ohio, Oregon, Texas and western Canada. Meteor radio echoes were heard as far away as the United Kingdom!

The Aurigids is one of several minor meteor showers that pepper the calendar and, for the most part, don't rate much attention from observers. However, this year the Earth was predicted to intersect a stream of dust produced by Comet Kiess around 83 BC, potentially leading to a meteor outburst. Unfortunately we only caught the very leading edge of the event, since the Moon rose around 10 pm and pretty soon was even washing out the stars. Still, pretty nifty that we saw any Aurigids at all, given that the outburst proper didn't happen until nearly dawn. And now I know what they were.

A Little Cantor Set in your Soul

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Via Jeff Masters, I read that this week a new record was set for least sea ice observed in the Arctic since satellite measurements began. Going by the NOAA polar webcam it has been raining at the North Pole.

At this rate, Russia may someday be a major naval power after all.

If anybody notices, any bets on whether the Bushies try to get polar sea ice data classified?

On a lighter note:

Me: Good thing I'm getting new sandals soon. The topology of my soles has recently changed.

Asad: That would have been much funnier if you'd been talking about your eternal soul.

Me: (...)

Me: The topology of my eternal soul would be hard to describe. It's uncountably holey.

Ba dum dum!

Imagery

Spent the weekend camping out in southwest Minnesota with telescopes, a borrowed and rather quirky car, and a somewhat incompetent (very much a theorist) presenting partner, bringing astronomy to the masses. Fun was had, on average. For some reason, passing all those Dairy Queens left me craving sweet frozen things, so one of the first things I did after unpacking was to make one.

Then I used the borrowed car to pick up my newly acquired arc welder. Which will be teh awesome.

The political blogs (and similar) have been generating some interesting imagery of late, mostly as a by-product of churning out high-grade snark. Examples:

Ezra wrote:

magine, for instance, that you came across a mime on a unicycle. Would you assume that this mime was inexplicably wedded to an ineffective form of transportation? Or that he thought looking hilarious on a unicycle would be good for his career as a mime?

Same with Kristol. You'd have to be a fool to look at the hornet's nest we've stirred up in the Middle East, the endless ground war we've entered in Iraq, [etc] and conclude, as Kristol does, that "[a]s for foreign policy in general, it has mostly been the usual mixed bag." Mixed bag of what? Nails and explosives?

Sam Boyd paints a lovely picture of my alma matter:

To start with, the idea of using the University of Chicago as a typical college experience is something like judging the experience of the average car owner by interviewing a guy in rural Idaho who drives a biodiesel-fueled Yugo -- he has his reasons and his choice is admirable, but it's also hardly typical. The UofC is a great place and I'm glad I don't go somewhere else, but it is a very odd place. We print t-shirts that say "where fun comes to die" and "hell does freeze over," and people who choose to go there are almost all very academically-focused and interested in ideas.

Michael Berube pens a hillarious meditation on third-party politics that includes the paragraph:

Of course, we don’t want to give Republicans too much credit for electoral smarts, especially since their current slate of candidates consists of the Mad Hatter, the March Hare, the Dormouse, some other lunatics, and Mister Excitement himself, James Gilmore. I’m just suggesting that the GOP neither demonized nor courted the Reform Party; it simply let Perot and the Perotistas disappear over the horizon and/or return peacefully to Zzyzzych 7.

And finally, I would be remiss if I failed to cite the newly-discovered Cheney Superposition (via Dean):


Quantum Cheney Superposition

Cats

Most of my high-level programming is done in Perl -- there are many reasons for this, but one is that it lends itself so well to flights of whimsy. For example, yesterday I was exceedingly delighted to find that this actually works:

use Quantum::Entanglement;

$gas = entangle(1, 'bottled', 1, 'released');
# gas now in states |bottled> + |released>

$cat_health = p_op($gas, 'eq', 'released',
sub {'Dead'},
sub {'Alive'});
# cat,gas now in states |Alive, bottled> + |Dead, released>

Speaking of cats, over at Dynamics of Cats we have ongoing summaries of a workshop on exotic solar systems, including tantalizing hints of possible terrestrial planet(s) next door at Proxima Centauri. Solar sail probe, anyone?


Okay, I'll go to bed now.

People in Flight

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For those in Minneapolis: go outside tomorrow evening at 9:50 and look west. Atlantis undocked from the International Space Station today and will be holding position about 70 km away until cleared to deorbit on Thursday (at the soonest). The pair should be a noteworthy sight.

For those elsewhere, you can always go here to find out when things will be passing over your location.

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On June 13 the ISS, with Atlantis docked, passed (roughly) over Minneapolis. It is a rather difficult target to photograph!

Zero-Tech Solar Still

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A solar still made with pottery-age technology, shown in cross-section.

Let's say you're stranded on a desert island, and you've found an outcropping of clay and a way to make fire, but your water supply is unreliable. You might make an item along the lines of the pot I've sketched here. Then you'd fill the outer ring with seawater, close the lid, and put more seawater in the depression atop the lid. Place in a sunny location or on the hottest sand you can find -- the coals of your campfire would probably work nicely, too. The point is to get the bottom hot, while evaporation keeps the lid cool, so condensation forms and drips into the central catchbasin. When finished, find a reed or similar to use as a straw and drink your freshly distilled water.

The caveat is that this is about the most inefficient way you could possibly do this, having no metal or glass to work with. In particular, since you're not recycling the latent heat of condensation, you have to supply the heat from outside. With solar energy this pot will be limited to around a tenth of a liter per day, so you'll have to make a bunch.

I think at least one reader knows why I'm posting this.

Stormy Weather

Intriguingly, there's a hurricane-force cyclone about to hit the coast of Oman. Over on the Weather Underground there's a long blog post about Cyclone Gonu by one of their meteorologists. While the BBC article claims that evactuations are underway, this could be a nasty event if the authorities haven't been paying attention:

Imagine that you live directly on the Gulf, but in a place where it hardly ever rains, and where a hurricane has never hit, for at least a generation -- for more than sixty years. Your community and many like yours are situated not only directly on the water, but near or in large dry riverbeds on the coastal plain, which is a narrow strip of sandy shoreline that is the dropoff for the three-thousand-foot mountain range behind it. ... And you don't have any idea what storm surge is...

Of course, most of the world is rather more concerned with the economic importance of this region, and after sideswiping Oman the cyclone is headed for Iran and the Straight of Hormuz. oil prices have been jumpy this week as a result. Again from the meteorology blog, a troubling note:

This is an unprecedented event. NO CYCLONE has ever entered the Gulf of Oman. And there are no custom 'storm surge' models available for that area. This forecast is based on my experience and subjective analysis of the seabed slope and storm surge interaction with the sea floor. Considering the region has never experienced a hurricane, let alone a strong one it is highly unlikely the loading facilities or platforms were constructed to withstand the forces

On the bright side, we've got plenty of troops in the Persian Gulf region who, I'm sure, would much rather help clean up after a hurricane than drive around dodging IEDs in Baghdad.

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Clouds gather over the old Pillsbury Flour sign.

Waay Down South

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McMurdo aerial view
An aerial view of McMurdo station taken by the NYANG.

Enjoy cold, the outdoors, and the prospect of working in the weirdest town on the planet? Just in case you're ever interested, this is where you'd go to apply for a job as support staff at McMurdo station in on Ross Island, Antarctica. Apparently "Craftspeople such as carpenters, electricians, mechanics" are in highest demand.

Last night I had a few beers with a collaborator who's been on four or five Antarctic ballooning campaigns, and he happened to mention that the drivers, cooks, mechanics, and other support staff make up the bulk of McMurdo's population. Which makes sense if you think about it. Lousy pay, but good benefits, free food and lodging, and nothing much to spend your money on anyway -- all US citizens are eligible to apply.

After Oil

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The Petronas Towers in Kuala Lumpur, one of the tallest buildings in the world. Wikimedia Commons

The end of cheap energy will be perhaps the central problem of the 21st century global civilization, impacting as it does every aspect of the infrastructure of global life -- how we move people and things around; how we power our technology; how we make stuff. Interconnectivity may make the world smaller, but high technology only gets you so far. After all, you can run all the computers in the world on solar energy, but refining every last scrap of organic matter on Earth into gasoline wouldn't power half the cars we have today. So you're left with the observation that when oil gets scarce, we'd better have another way of getting supplies to the plant that makes the solar panels and food to the people that run the computers, or the whole system grinds to a halt.

Probably in the ugliest way possible.

James Howard Kunstler has been getting attention for the New Urbanists for a while now with titles like The Geography of Nowhere and The Long Emergency, the latter of which deals precisely with the consequences of cheap energy being a historical anomaly. I highly recommend either book, but for a shorter version, he gave an excellent speech to the Commonwealth Club of California the other day, available here as text or MP3.

Peak oil is a provocative tautology only because it runs against two centuries of abnormal experience:

Oil production in the US peaked in 1970. ... In 1970, we were producing about 10 million barrels a day. Now we're down to less than five -- and we consume over 20 million barrels a day. We have compensated for that since 1970 by importing oil from other nations. Today we import about two-thirds of all the oil we use. Today, the world is consuming all the oil it can produce. As global production passes its own peak, the world will not be able to compensate for its shortfall by importing oil from other planets.

The oil industry has been dominated by what are called supergiant fields. ... The Burgan field of Kuwait, the Daqing of China, Cantarell of Mexico, and Ghawar of Saudi Arabia. Together in recent decades they were responsible for 14 percent of the world's oil production, and they are now in decline. ...

Both The North Sea and Alaska are now past peak and in depletion. Prudhoe Bay proved to be Alaska's only super giant oil field. ... Now 57 of Norway's 69 oil fields are past peak and the average post-peak decline rates average 17 percent a year. The UK's share of the North Sea has declined to the extent that England is now a net energy importer. ...

Russia, despite current high levels of post-Soviet-era production, peaked in the 1980s ... Iran is past peak. Indonesia, an OPEC member, is so far past peak it became a net oil importer last year. Venezuela is past peak.

As a result, the size of modern things becomes a problem:

The key to all our everyday activities in the future is scale. We will probably have to live more locally than has been the case in recent decades. I think we can state categorically that anything organized on the gigantic scale, whether it is an agricultural system, or a finance system, or a corporation, or a chain of stores, or a school, or a government, is going to run into trouble. ...

Our hyper-gigantic cities and so-called metroplexes are a pure product of the 200-year-long upward arc of cheap energy. Like other things of gigantic scale, our cities will get into trouble. They are going to contract substantially. The cities that are composed overwhelmingly of suburban fabric will be most susceptible to failure. Orlando, Houston, Atlanta. The cities that are overburdened with skyscrapers will face an additional layer of trouble -- the skyscraper, like the mega-city, was a product of cheap energy, and we are going to have trouble running them, especially heating them without cheap natural gas.

Not surprisingly, China is mentioned a number of times in this talk. I'm fascinated by the architectural revolution going on there (here's an interesting gallery examining some of the highlights). Like it or not, China is modernizing and needs to make room for huge new urban populations, and accomodate enormous new demands on its energy resources. So you have two countervailing trends linked by a common aspiration to grandiose scale: on the one hand the cities are being built out along current Western lines, which all the disastrous long-term impacts that will entail (i.e. see above); on the other, the Chinese (unlike, say, America of 50 years ago) are well aware of this reality and are pushing for development along more sustainable lines. It will be interesting to see if the developing world can leapfrog entirely past the age of suburbia.

The desire for enormity of scale is hardly unique to China, of course. Anyplace that wants to emphasize its membership in the global civilization will be tempted to pursue the grand. Huge, after all, is easy to confuse with permanent. Thus the present run-up of supertall buildings throughout the eastern hemisphere. 15 of the 20 tallest skyscrapers are currently on the Pacific Rim, and of those, 12 were built in the last 10 years. Burj Dubai is under construction. Numerous 600+ meter towers are in various stages of planning. Kuwait's Mubarak al-Kabir tower is a particularly striking example, that would rise to over a kilometer in height if it gets built.

Nor is the good old United States immune to the tendancy towards gigantism -- when complete, you'll practically be able to see the Chicago Spire from here! Many of these new projects, you'll notice, intend to bring offices and high-rise residences into proximity as virtual arcologies, part of a conscious effort to increase urban core density and reduce commute distances. While this is a goal Kunstler is actually working to advance, the concern is that doing so by way of these high-tech, vast-scale new buildings isn't really sustainable. However, several of the buildings I've cited here consider low energy and ecological impact as explicit design goals -- more of them will have to reach completion before we can really evaluate how well they do in that respect.

Reminder: Lunar Eclipse Today

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Urban Winter '06-'07: Droplet
The icicles today have been amazing. Click to enlarge -- really, do. It's worth it.

Just a reminder that there's a total lunar eclipse tonight. It's actually starting right about now, so if you're in North America just look east as soon as the moon rises.

Time for Time

This afternoon I'll be skipping the weekly physics colloquium in favor of a symposium at our own (admittedly not creatively named) Institute for Advanced Studies on "Big History". So if anyone cares to join me over in Nolte at 4 pm:

Mapping Timescales - presentation by David Christian and David Fox

Sponsored By: Institute for Advanced Study

David Christian (History, San Diego State University) and David Fox (Geology and Geophysics, University of Minnesota) will discuss the emerging field of "Big History," which combines the evolution of the planet with human history.

Astronomers, of course, have a congenital affinity for long timescales, but you folks may have noticed my deep interest in projects like the Long Now Foundation. On which topic, the New York Times this week has a profile of Stewart Brand, one of the principals behind the Clock of the Long Now. However, he's made a successful career of being uncannily right about the near future as well, and I recommend giving it a read. Incidentally, the big mechanical thing he's posing with is a prototype of the chimes for the Clock, which like the rest of the beast are a mechanical digital beast able to generate millions of unique chiming sequences over the Clock's 10,000 year lifespan.

Observation: 10,000 years is roughly the length of time that of Stonehenge has been a significant site. The oldest post-holes there have been dated to c. 8000 BCE, although perhaps five millenia more passed before the first stones were erected.

Also from this week's NYT, a decent overview of fringe fusion ideas. Fusion power has had this nasty habit over the past half-century of always being about 30 years from practical, which is as good an argument as any for exploring many alternate paths to getting it to work. Most will fail, but only one has to work out to dramatically ease humanity's long-term outlook.

Naked Eye Nova

Passed along for your interest: there is a magnitude 3.7 nova in Scorpius. (Via Bad Astronomy)

Scorpius being a rather southerly constellation, it never gets more than 12 degrees above the horizon here in Minnesota (and that right about at sunrise), so I don't plan to attempt an observation. Still, fundamentally cool.

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