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How tide predicting, analog computers won World War II

Without Lord Kelvin, there would have been no D-Day.

There's some very cool science history in the September issue of Physics Today, centering around a collection of analog computers, developed in the 19th century to predict tides. This was a job that human mathematicians could do, but the computing machines did the job faster and were less prone to small errors that had big, real-world implications. David Kaplan, an assistant professor in the University of Wisconsin-Milwaukee physics department, sent the links over. He says that these machines ended up being crucial and are a big, in-your-face reminder of the complications of living in a world without calculators:

"... it was particularly important during WWII in order to properly plan beach landings, but even without the war part I found it fascinating. We take this so for granted now, that we can crank out sin() and cos() values instantly, but that was not always the case."

We're talking about predictions a bit more precise than simply saying, "the water is low" or "the water is high." Physics Today explains why the behavior of tides was so important at D-Day and why the tide calculators were so important to Allied success.

As an Allied cross-channel invasion loomed in 1944, Rommel, convinced that it would come at high tide, installed millions of steel, cement, and wooden obstacles on the possible invasion beaches, positioned so they would be under water by midtide.

The Allies would certainly have liked to land at high tide, as Rommel expected, so their troops would have less beach to cross under fire. But the underwater obstacles changed that. The Allied planners now decided that initial landings must be soon after low tide so that demolition teams could blow up enough obstacles to open corridors through which the following landing craft could navigate to the beach. The tide also had to be rising, because the landing craft had to unload troops and then depart without danger of being stranded by a receding tide.

There were also nontidal constraints. For secrecy, Allied forces had to cross the English Channel in darkness. But naval artillery needed about an hour of daylight to bombard the coast before the landings. Therefore, low tide had to coincide with first light, with the landings to begin one hour after. Airborne drops had to take place the night before, because the paratroopers had to land in darkness. But they also needed to see their targets, so there had to be a late-rising Moon. Only three days in June 1944 met all those requirements for “D-Day,” the invasion date: 5, 6, and 7 June.

You can read more about tide predicting machines on Wikipedia, and try out a Java simulation of Lord Kelvin's tide predicting machine at the American Mathematical Society website.

Volcanic vent surprise

What are all those frothy bubbles rising from the sea floor and coating the submersible craft in this video? Why, it's liquid carbon dioxide, venting off an underwater hot spring connected to Eifuku volcano in Japan's Volcano Islands.

Better yet, life can still survive, even in an environment this extreme. Check out what blogger Caleb Scharf spotted:

... pay attention at 38 seconds into the show. With utter disregard for the extraordinary environment a shrimp-like creature swims purposefully under the robot and exits stage lower right. It may not live in liquid CO2, but it doesn’t seem bothered by it in the slightest. We must also assume that it’s finding plenty of food within this bubbling environment.

Video Link

Via Ed Yong

A submarine named Alvin

I've been traveling for the last couple of weeks. One key stop: Woods Hole, Mass., where I got up close and personal with everybody's favorite research submarine. Originally commissioned in 1964, Alvin is currently disassembled as part of a regular maintenance inspection and overhaul. I got to go behind-the-scenes to check out Alvin and the RV Oceanus—a research ship also operated by the Woods Hole Oceanographic Institute. This is a window on Alvin's old manned pod, a massive sphere that can hold two scientists. It's being replaced in the current retrofit, and this sphere will go to the Smithsonian. More photos to come ...

Human disease kills coral

In news that would be completely fascinating, were it not so damn depressing: One of the causes behind Caribbean coral die-offs seems to be a bacteria, spread from humans to the coral through sewage. It's the first time that a human disease has ever been shown to kill an invertebrate.

Japanese tsunami and the birth of icebergs

Scientists have long speculated that large tsunamis could be linked to the calving of icebergs—where chunks of ice break off of the side of a glacier or ice shelf and float away. The Tohoku earthquake and tsunami that happened in March off the coast of Japan finally gave them much more direct evidence of this phenomenon. Fascinating stuff, and a great reminder of how interconnected the world really is.

Video Link

Via Jeremy Hsu

Algae beach party

Beachgoers in Qingdao, Shandong province, China, were met with a fuzzy, green blanket of ocean last week, as the water there exploded with algae.

You've heard before about dead zones. These are patches of coastal ocean where river runoff full of fertilizer chemicals have produced massive algae blooms. As the algae die, their decomposition reduces the oxygen level of the water to the point that many fish and other aquatic life can no longer live there.

This is what a dead zone looks like, just before the death.

It's worth noting, when I pulled this photo out of the Reuters files, I could see similar shots, taken on the same beach, in 2010, 2009, and 2008. This isn't a fluke. It's an endemic problem.

Image: REUTERS/China Daily China Daily Information Corp - CDIC

Swim goggles made from fish scales

Neat post about an experimental plastic substitute made from fish scales over at Brian Lam's ocean-themed blog Scuttlefish. So far art student Erik de Laurens "has made not only goggles, but eye-glass frames, drinking cups, and a wooden table with a fish scale inlay" from fish scales.