- Farewell Discovery: Longest-Lived Shuttle’s Greatest Hits
- Genetic Errors Nixed Penis Spines, Enlarged Our Brains
- Tiny Fibers Put the Head on Stout Beer
Posted: 09 Mar 2011 01:27 PM PST
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The space shuttle Discovery returned to Earth for the last time this morning, ending its reign as the world's longest running and most-traveled spaceship.
"It just played out the way we wanted it to," said Kennedy Space Center Director Bob Cabana in a press conference after the landing. "We wanted to go out on a high note, and Discovery has done that. We couldn't ask for more."
When it touched down at Kennedy Space Center in Florida at 11:57 EST on March 9, 2011, Discovery had flown 39 missions, spent a full 365 days in space, orbited the Earth 5,830 times and traveled more than of 148 million miles. It has carried 246 people into space, more than any other vehicle, including the first woman to ever pilot a spacecraft, the oldest person to fly in space, the first African-American to perform a spacewalk and the first sitting member of Congress to fly in space.
The shuttle's 27-year career hit several of the highlights of the space program, including delivering the Hubble Space Telescope to orbit in 1990 (and fixing it twice), carrying a 77-year-old John Glenn back into space in 1998, and leading NASA's return to space after the loss of Challenger in 1986 and Columbia in 2003.
On its final flight, the shuttle linked up with the International Space Station to deliver a new spare room full of supplies and science experiments, plus bring the first human-like robot into space.
"We're going to miss Discovery," International Space Station commander Scott Kelly told shuttle commander Steve Lindsey on Sunday, before Discovery's crew left the space station. "Discovery has been a great ship, and has really supported the International Space Station, more so than, I think, any other space shuttle. And we wish her fair winds and following seas."
Now that it's back on the ground, Discovery will retire as a museum piece at the Smithsonian. Here we look back at the veteran spacecraft's high points as the shuttle era draws to a close.
Posted: 09 Mar 2011 11:44 AM PST
Geneticists have linked the physical appearance of humans to patches of DNA lost in the 5 million years since we shared a common ancestor with chimpanzees. One loss prevented men from growing penile barbs, which chimps possess. Another enlarged some regions of our brain.
"We can know what makes us human, what makes us physically different from other animals and why," said developmental geneticist Gill Bejerano of Stanford University, an author of the March 10 study in Nature.
Only 2 percent of the DNA in our genome forms protein-coding genes. The rest, once called "junk DNA," helps control and coordinate gene activity. Out of this regulatory coordination, physiological complexity emerges.
Bejerano's team started by comparing the genomes of chimpanzees and macaque monkeys, which last shared a common ancestor 20 million years ago. They identified regions that hadn't changed in chimps, then compared these to corresponding stretches of the human genome. They found more than 500 mutations known as deletions, or stretches of DNA present in chimps but lost in humans.
Two deletions, one near a male hormone-signaling gene and another near a neural development gene, were especially intriguing. Tweaking those genes in mice suggested possible roles for the loss: eliminating penile spines and boosting cerebral cortex growth.
Bigger brains are an obvious advantage ("It probably helped us become the thinkers we are today," Bejerano said), but it's unclear why evolution weeded out the spines. These tiny, hair-like projections, found in male chimps and cats, can trigger female ovulation. They also increase sensitivity and remove existing sperm, ostensibly giving males a reproductive advantage. Bejerano suspects the spines are conducive to monogamy.
Could restoring the relevant regulatory DNA in humans resurrect penile spines? "I'm going to leave it to others to paint that picture and its consequences," said evolutionary biologist Sean B. Carroll of the University of Wisconsin, who wasn't involved in the study. "But my guess is that something would probably happen."
More practically, the findings underscore the importance of regulatory changes to human evolution. "Regulation is a choreograph critical to shaping how organisms appear. This research is going to be a hot trail to follow," said Carroll. "It's not just about what genes you have, but how they're used."
Image: Picture Taker 2/Flickr
Citation: "Human-specific loss of regulatory DNA and the evolution of human-specific traits."
Posted: 09 Mar 2011 11:19 AM PST
Irish mathematicians have discovered tiny plant fibers can make nitrogen bubbles out of stout beer and form a creamy head of foam. The find could mean an end to more expensive and less-eco-friendly technology currently used to create fizz.
Nitrogen-infused stouts are known for their long-lasting and creamy heads, a feature that carbonated beers can't emulate. But nitrogen doesn't froth up on its own, so to get foam on a canned stout, brewers insert a widget — a small plastic ball with a hole in it. When a can is opened, the widget releases pressurized nitrogen into the beer, which then triggers more dissolved nitrogen in the beer to bubble out.
But a graduate student supervised by applied mathematician William Lee at the University of Limerick in Ireland discovered that microscopic plant fibers made of cellulose, such as cotton, can also froth up a stout.
"What happens around these fibers is really complex, so it's a ripe area for research," said Lee, who posted his team's research March 2 on arXiv.org. "This is also a matter of national pride. Stout beers are as culturally important to Ireland as champagne is to France."
Carbon dioxide dissolves into beer during the brewing process, and the gas quickly nucleates to form bubbles in the liquid with the help of special surfaces. Microscopic plant fibers that hide in drinking glasses are especially good at bubbling up carbon dioxide because they trap small air bubbles that make for excellent nucleation sites. But carbonated brews form large, fragile bubbles and heads that quickly fizzle out.
To create longer-lasting and creamier heads in stouts, brewers pump the beer full of nitrogen because the gas forms smaller, more stable bubbles without affecting taste. A tiny opening in the nitro bartaps forces nitrogen into stouts as the beer is poured, but canned stouts are trickier because plant fibers don't help nitrogen bubble out. Or, so beer experts thought.
Lee and his team recorded stouts under a microscope (video above) to watch bubbles form inside cellulose fibers. They discovered the bubbling rate was up to 20 times slower than in carbonated brews, which is probably why no one had noticed it before.
"If you line a can with enough of them, you can get a creamy head in less than 30 seconds," Lee said, roughly the time it takes to open and pour a stout.
It takes roughly 4.3 million microscopic fibers to accomplish the feat, which translates to a postage-stamp-sized pad of fibers. Food-safe cellulose should be cheaper than widgets to put into cans, Lee said, especially since the latter require a de-oxygenation process to prevent spoiling the beer.
Lee and his team hopes their discovery will make stouts slightly cheaper (on the order of a few cents per can), in addition to creating new research leads in fluid mechanics.
Video: Pockets of air trapped in tiny cellulose fibers, each between 10 and 50 microns wide, help nitrogen and carbon dioxide bubble out. Courtesy of Michael Devereux/Mathematics Applications Consortium for Science and Industry
Image: A plastic widget found in a can of Guinness stout beer. slworking2/Flickr
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