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Indianapolis Executive Airport is a small, single-runway airfield that serves Hamilton County northeast of Indianapolis. On June 14, while driving to my parents' house to celebrate Father's Day and my sister's birthday, I happened to pass the airport during an open house benefiting the Indiana Down Syndrome Foundation. The event gave me a close look at three interesting helicopters: a Vietnam-era Huey, an Indiana State Police "eye-in-the-sky", and an air medical transport.

The Huey, serial number 70-16369, was an Army air ambulance deployed to Vietnam in 1971. It returned in 1972 and continued to perform air evacuations in South Carolina, Texas, Illinois, and Ohio until the Army retired it in 2001. At that point, the army transferred ownership to the not-for-profit Down East Emergency Medicine Institute in Maine, which used it for emergency search and rescue. In 2005, brothers John and Allen Walker purchased the helicopter, trailered it 1,300 miles to Peru, Indiana, and formed the not-for-profit American Huey 369 Organization to preserve the aircraft.

The Huey still flies, and one can purchase "memberships" that allow one to go on rides. When I arrived at the airport, the pilot was preparing to take a load of new members into the air.

I desperately wanted a turn. I spoke to an attendant and filled out one of the membership forms, only to be turned away when I pulled out my credit card. They only accepted cash or check.

An Indiana State Police helicopter, a Bell L3, number N54SP, was parked near the Huey. It is one of three helicopters in the state police's fleet of 14 aircraft. The pilot said he and the helicopter had come directly from helping helping flood victims south of Indianapolis.

A 1985 Eurocopter BK117, number N112LL, came last in the line of helicopters. It is one of four Lifeline helicopters operated by Clarian Health. Since 1979, it and the other Lifeline helicopters have transported more than 29,000 patients. The pilot said he averages about one flight per day and can range up to 150 nautical miles.

The back of the helicopter opens completely to allow access to the gurney. As one might expect, the cabin is filled with all sorts of medical supplies.

It was fortunate that I stumbled upon the open house. I found it fascinating to see these purpose-built machines up close and to talk to the pilots and crew.

Allerton Park is a 1,500-acre wooded nature preserve about 40 minutes southwest of Champaign. The University of Illinois administers the park and uses it for conferences, academic retreats, and teaching. Yesterday, Yun-young, Manish, and I went hiking on two of its nature trails. Afterward, we stopped at the day's geohashing coordinates, which were only about two miles away.

We first passed through the meticulously-groomed formal gardens.

Then we entered the peaceful and shadowy nature trail. I periodically pointed out the trees I recognized and the animal tracks that crossed the path.

Eventually, the trail curved to follow the Sangamon River.

It was obvious from the muddy trail and lack of groundcover that the river had recently flooded the area.

We had to detour around standing water or ford small streams several times. The moisture also meant that we had to constantly fight off swarms of mosquitoes. Unfortunately, I had forgotten the insect repellent. When we passed through sunbeams I could see dozens of the insects buzzing around our backs and unprotected arms. At one point, Manish killed five mosquitoes with one slap. Today my shoulders and elbows are covered with red welts.

Despite that, we all enjoyed the hike. The forest was lush and beautiful, and I found it fascinating to see the effects of the flood.

We made it to the opposite end of the park and returned along the higher and dryer access road. We passed a family attempting to break into their car, having locked their keys inside. I called AAA for a nearby service station, but the father decided to break a back window instead. That idea excited his young daughter who enthusiastically ran into the woods to find a big rock. We left before she found one.

After returning to my car, we circled the park to the day's geohashing coordinates. In a drastic departure from previous coordinates, which fell in cornfields, Saturday's coordinates fell in a soybean field. I placed a marker flag while Manish and Yun-young took some pictures. Unfortunately, we arrived late and did not meet any other geohashers.

It was a fun day trip, and all three of us look forward to exploring the rest of Allerton south of the river.

Yun-young posted her pictures in this Facebook album.

Threads, on the other hand, are wildly nondeterministic. The job of the programmer is to prune away that nondeterminism. We have, of course, developed tools to assist in the pruning. Semaphores, monitors, and more modern overlays on threads offer the programmer ever more effective pruning. But pruning a wild mass of brambles rarely yields a satisfactory hedge.

To offer another analogy, suppose that we were to ask a mechanical engineer to design an internal combustion engine by starting with a pot of iron, hydrocarbon, and oxygen molecules, moving randomly according to thermal forces. The engineer’s job is to constrain these motions until the result is an internal combustion engine. Thermodynamics and chemistry tells us that this is a theoretically valid way to think about the design problem. But is it practical?

To offer a third analogy, a folk definition of insanity is to do the same thing over and over again and to expect the results to be different. By this definition, we in fact require that programmers of multithreaded systems be insane. Were they sane, they could not understand their programs.

From The Problem with Threads by Edward A. Lee.

Alejandro's picture of my halloween costume is currently the fifth result for [WARNING: don't click these links if you are squeamish!] "shark attack" and the first result for "shark attack victim" on Google Image Search.

The doodles that I draw in the margins of my class notes are second and third on a search for "geometric designs", but they don't bring in as many visitors.

Finally, my pictures of Champaign's many construction projects are the third and fourth results for "champaign construction", right behind a superb local photoblog.

These results do not necessarily say anything about my website, just that Google likes images with meaningful filenames and descriptive alternate text.

Champaign's May 31 geohashing coordinates fell between the runways at Willard Airport, so I could not have made it without breaking several trespassing laws. Fortunately, I was also driving to Chicago for a concert, so I could take the back roads past Aurora, Illinois' graticule instead. The coordinates fell in a remote region of farms about an hour and 45 minutes directly north of Champaign.

The drive was sublime. The sky was clear, and the fields were just beginning to turn green. I had the windows and sunroof open the entire time.

Near Gibson City I saw dozens of wind turbines spinning on the horizon. I turned and drove to get a closer look. They were further away than I had expected; I drove at least five miles before meeting the first.

As I got closer, more and more turbines appeared over the treetops.

I had no idea that such a large wind farm existed so close to Champaign. According to Horizon Wind Energy, the Twin Groves Wind Farm, of which I saw only a part, covers 22,000 acres and produces 396 megawatts with 240 turbines. The American Wind Energy Association says that Twin Groves produces about half of Illinois' wind power.

After driving among the windmills like an ant among giant flowers, I resumed the trip north to the geohashing coordinates. The precise point fell in a cornfield near Campus, Illinois, population 145. To reach the field, I drove down a poorly-marked but well-maintained gravel road.

I was not surprised that no other XKCD readers were there since I arrived about 30 minutes late and the coordinates were so far away from everything. I did not hike into the field this time.

A pickup truck passed as I was getting back into my car. The driver rolled down his window and asked if anything was wrong. I thought about how I could explain geohashing but instead told him I just stopped to take some pictures.

From there, I slowly made it back to the main roads and arrived in Chicago in time for the concert.