03/27/2002
Survival Under Pressure
Did you watch The Players Championship at Sawgrass here in Florida last Sunday? If not, you missed one of the most amazing finishes of a professional golf tournament in history. Craig Perks, co-leader going into the final round on Sunday, was spraying bogeys all over the place squandering his lead. He even missed two one-foot putts! Obviously, the pressure was just too great for this player, ranked 203 in the world and whose only tournament win was on the Hooters Tour! I never heard of the Hooters Tour, have you? But Perks perked up on the 16th hole, where he holed his chip shot from off the green for an eagle. On the famed 17th, the green a tiny target in an alligator-infested lake, he canned a 25-foot birdie putt. Now in the lead again, he began the 18th hole with an errant drive. After clearing the crowd for a stupid attempt to shoot through the trees, he finally paid attention to his caddy''s advice to lay up. The crowning touch was another holed chip from off the green for a par.
I was reminded of my round at Spooky Brook in New Jersey some years ago when I chipped in on three out of the first six holes, the last shot being from 125 yards out. I enjoyed those 6 holes more than my hole-in-one. (Longtime readers will have anticipated that I wouldn''t miss the chance to work in my hole- in-one here.) Only in my case, there wasn''t a $1,080,000 first place finish on the line!
Intense pressure can certainly affect people and other things differently. In Perks'' case, it could be said that he was choking under the pressure until those last glorious holes. In science, the study of materials under intense pressures has led to some very interesting results. My own appreciation of the possibilities of high-pressure research came when workers at General Electric first used high pressure to make diamonds in the laboratory. Today, their process is used to make industrial diamonds.
Actually, diamonds are the key materials use in an apparatus to attain some truly phenomenal pressures. What kind of pressures? We''re talking pressures as high as in the center of the earth, something on the order of 4 to 5 million times atmospheric pressure (we call this 4 to 5 million atmospheres). At such pressures, strange things can happen. For example, hydrogen becomes a metal! For those who are uncomfortable with pressures expressed as atmospheres, it might help to note that an atmosphere is equivalent to 14.7 pounds per square inch (psi).
Let''s now make a diamond anvil high-pressure apparatus. It''s really pretty simple. First, we take two diamonds and polish down a flat face on each one. These faces are typically about a millimeter in diameter. Now let''s glue them to a couple of big metal cylinders in a piston arrangement that lets us screw down on the cylinders to bring the diamond faces together. Now all we have to do to get our extremely high pressures is just screw those diamond faces together real tight. Why don''t we use something else instead of diamond, say stainless steel? It turns out that most materials either fracture or deform or break down in some manner under extreme pressure. Diamond''s legendary hardness, however, lets it hold up fantastically well.
You may be wondering how do we get such high pressures in such a simple apparatus? To illustrate the principle, let''s say you weigh 150 pounds. Now, stand on a platform, analogous to the piston, with a diamond glued to the bottom having a one-inch square face. Ok, that''s a huge diamond but, assuming you could balance on it, the pressure would be 150 pounds per square inch (psi). Since one atmosphere is about 15 psi, you have generated a pressure of roughly 10 atmospheres between the diamond and the floor. Now suppose the diamond face is just a tenth of an inch square. That''s only 0.01 square inches in area. Now, our 150 pounds has generated 150 divided by 0.01 or 15,000 psi. That''s about a thousand atmospheres pressure. In other words, if you squeeze on something small, you can magnify the pressures to quite high values. This is what''s done in the diamond anvil - screw down hard on those small diamond faces.
Of course, the apparatus to do this is more complicated than I''ve described and to measure what goes on in the material getting squeezed is tricky. The diamond anvil has an advantage that can be quite useful. Being transparent, you can look through the diamonds with a microscope and watch what''s going on. You can also make spectroscopic measurements.
Aside from Craig Perks, what prompted my concern with pressure was an article in the February 22 issue of Science. The article is by Anurag Sharma and coworkers at the Geophysical Laboratory, Carnegie Institution of Washington and is titled "Microbial Activity at Gigapascal Pressures". (The Pascal is just another unit of pressure.) What these researchers did was to look at what happens to bacteria when they squeezed the bejeebers out of them. To do this, they formed a film of water and bacteria between the two diamonds in the diamond anvil apparatus and squeezed down on those little microbes. The pressures they obtained were equivalent to those that would be found if you had an ocean around 90-100 miles deep. I calculate the pressures to be roughly about 10 thousand atmospheres.
Bacteria are pretty sturdy critters and have evolved to survive under some really harsh conditions - deep underground in rocks, in hot boiling springs, in highly acid or salty conditions in Antarctic ice, etc. Could bacteria survive in the polar ice caps on Mars or what is believed to be a frozen ocean many miles thick on Europa? Those are the types of questions these anvil experimenters hope to answer. So far, the bacteria turn out to be surprisingly hardy creatures.
These workers studied a couple types of microbes, one being the familiar E. coli that we all harbor in our guts. At the highest pressures, of the initial million or so bacteria, about 10,000 lived to tell the tale. How do you tell that these 10,000 are still alive? You don''t just look at them through a microscope; you also monitor with dyes and spectroscopy the products of the microbes'' metabolism. At a certain pressure the liquid water turned to a high-pressure form of ice. The microbes, or at some of them, still seemed to adapt to this change of habitat. There was, however, a limit to how much pressure these little critters could take. At that critical pressure, the spectral data showed no more evidence of metabolism. However, the researchers conclude that, at least as far as the pressure is concerned, any E. coli on Europa or Mars could hack it. Of course, there are other factors and we still have a bit of work to do, like actually finding microbes on these distant bodies.
There are as usual the skeptics who question most new work. In this case, they question whether the bacteria were indeed "alive" after being subjected to the anvil treatment. As reported in another article in Science commenting on this work, Jennifer Couzin reports that these skeptics want to see the bacteria grow and multiply. They feel that just showing the critters to be mobile and metabolic isn''t enough. This research is apparently in the works.
Some informed readers might say, "Why all the fuss? The effect of pressure on bacteria has been known for over a century." And they would be right. Just search "high pressure food processing" on your search engine and a plethora of sites show up. The use of high pressures to kill undesirable microbes in milk, for example, was reported in the early 1900s. However, the actual utilization of high pressures commercially seems rather limited at this point. I have not made a thorough search of the Web on this subject so must say that I could be unaware of some widespread application.
I think the real point is that, while the food industry is concerned with reducing the level of unwanted microbes in our food, the diamond anvil workers are more in tune with today''s trend in the media. These researchers are more interested in the few that survive under pressure. By chance, I too have developed a keen interest in high pressures, in this case my own recent elevated blood pressure readings in this laid back Marco Island atmosphere. Hopefully, returning to New Jersey next week and working on my tax returns will straighten out my problem. Yeah, right!
Allen F. Bortrum
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