Sunday, 26 September 2010

Johnald's Fantastical Daily Link Splurge

Posted: 24 Sep 2010 01:28 PM PDT

Bright sand streaks can form in the wake of desert cyclones when the whirlwinds break up popcorn-ball-like clumps of sand, a new study shows. The first-ever sighting of bright, instead of dark, dust-devil tracks on Earth could help decipher how these funny features form on Mars.
"This is the first observation and analysis of bright dust-devil tracks on Earth," said geologist Dennis Reiss of Westfälische Wilhelms Universität Münster in Germany, who led the new study. "They are known from Mars, but their formation mechanism is unknown."
Scientists have spotted dust-devil tracks in satellite images of both Earth and Mars, and the Mars rovers Spirit and Opportunity have even seen the dusty cyclones whipping past.
Most of these streaks are darker than the surrounding sand. The coarser the grains of sand are, the darker they appear. When dust devils swish by, they clear their paths of smaller grains, leaving dark tracks like eerie, swirly tattoos. But occasionally, cameras orbiting Mars have caught glimpses of bright streaks on dark sand.
"They have posed a problem," said planetary scientist Ronald Greeley of Arizona State University, who has researched how dark dust-devil trails form on Mars. "How would that mechanism" — blowing small grains aside — "work with the bright streaks? That's been the puzzle."
Reiss and colleagues may have found an answer in the Turpan desert in northwestern China. The crew went there to hunt for dark dust-devil tracks on the ground. Until their field study, such tracks had been seen only from orbit. They found several of the dark tracks and published an "up close and personal" analysis in the July 28 Geophysical Research Letters.
But on April 18, the team saw several active dust devils leaving surprisingly bright tracks. "It was good luck," Reiss said.

When they looked closer, the researchers realized the streaks weren't actually any brighter than usual — they were filled with the same coarse, millimeter-size sand that dust devils normally suck clean. But the surrounding sand had been darkened by five minutes of rainfall the previous night.
The rain had cemented bits of sand, silt and clay into clumps up to a centimeter wide. When the dust devils came through, they destroyed the fragile clusters, revealing the finer sand grains below. The dust devil tracks appeared bright in contrast to the rain-darkened background. The results will be published in an upcoming issue of the journal Icarus.
While there is obviously no rain on Mars, landers and rovers have observed similar clumps that are held together by electrostatic forces. In 1979, Greeley conducted lab experiments showing that charges build up on dry, wind-blown sand particles in a similar manner to the way charge builds up on a balloon when you rub it on your hair. Just like the charged-up balloon can stick to the wall, charged sand grains pull together to form delicate, "popcorn ball" aggregates.
"The destruction of aggregates on Mars would lead also to bright dust devil tracks," Reiss said.
Greeley thinks the idea makes sense. "This is a plausible model for the formation of the bright tracks on Mars," he said. "This is a very nice study, a very nice result."
Images: 1) Bright dust-devil tracks in China. Dennis Reiss/Icarus. 2) Dust-devil track imaged by the HiRISE camera on the Mars Reconnaissance Orbiter. NASA. 3) Microscope images of the clumps of sand, silt and clay that darken the landscape around the bright tracks. Dennis Reiss/Icarus.

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Posted: 24 Sep 2010 10:53 AM PDT

By Ed Grabianowski, io9
We usually think of terraforming as something we'll do in the future to other planets, but we have thousands of years of experience changing the shape of our own planet in profound ways.
The term "terraforming" was invented by author Jack Williamson in his 1942 short story "Collision Orbit," published in Astounding Science Fiction. In the intervening decades, its literal meaning ("Earth forming") has shifted. It still commonly refers to the speculative act of altering non-Earth planets to make them habitable by humans. But anything that drastically changes geography to suit human interests can be called terraforming, even if it happens here on Earth. If only we all had the same interests.

Destructive Terraforming

Humans have been shaping and changing the Earth for thousands of years, sometimes for the better. All too often, though, our terraforming methods have been destructive – sometimes so destructive that they seem like the opposite of terraforming. Mountain top removal mining, for instance, blows the top off of a mountain and fills a nearby valley with the polluted debris. The resulting blasted landscape looks more like we're turning Earth into Mars than the other way around. Maybe we should call it deterraforming. This series of NASA LANDSAT images (below) shows the Hobet mine gradually obliterating a large swath of West Virginia over the course of about 25 years.

Dams radically alter geography by diverting rivers, creating artificial lakes and changing flood patterns. We've had lots of practice – some Middle Eastern dams are four or five thousand years old, and dams dating to the Roman Empire not only still exist, they still function perfectly well. Modern dams are chart-toppers when it comes to the amount of real estate terraformed. Shasta Dam (below) in California blocks the Sacramento River, creating Shasta Lake. The lake covers almost 50 square miles. What was once a verdant valley ecosystem is now completely under water. Change on that scale has happened at the sites of dozens of large dam projects worldwide.

Cities and populations

Cities, of course, aren't built in a few months, and they don't generally change geography instantly. But every city changes the landscape in a thousand small ways that all add up: leveling terrain for construction projects; shifting waterways for drainage; paving over huge areas; tunnel systems for transportation and infrastructure; the heat island effect. If you could somehow strip away the city and see the land beneath, it would look vastly different from how it did before the city was there.
If we talk about cities and population growth as a part of terraforming, we have to talk about the most pervasive, long-term terraforming project ever undertaken – the introduction of huge quantities of greenhouse gases into the atmosphere. That is ultimately how we'll terraform Mars, if we do it, so we've established an interesting test case here on Earth. Increased global temperatures and decreased polar ice levels would be an important first step in terraforming another planet. If we keep at it for another hundred years or so, we'll have a better idea of how it'll play out.
Of course, it's easy to look at all these "detrimental" terraforming methods purely as environmental evils, but everything has a benefit that we're apparently willing to pay the price for. The irrigation, flood control and power generation provided by dams has been significantly helpful for humans. Our desire for cheap on-demand electricity leads to mountain top removal mining, and how many of us would be willing to forego air-conditioning for the next ten years to save a West Virginia mountain?
There's only one sure thing about terraforming: when you change a planet, there will be consequences, and not always the consequences you expect. We'll get deeper into unintended consequences in part two of this series, when we examine more constructive terraforming methods.
Images: 1) Carajás Mine, Brazil/NASA Earth Observatory. 2) NASA Earth Observatory. 3) Shasta Dam/U.S. Bureau of Reclamation.

Sources: NASA Earth Observatory. "Mountaintop Mining in West Virginia." National Performance of Dams Database. "Dam Name: Shasta."
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Posted: 24 Sep 2010 10:13 AM PDT

The Smithsonian National Zoo now has two litters of extraordinarily cute lion cubs to look at via webcam, after the birth of three new cubs on September 22.
These new cubs are closer than half-siblings with the cubs we have been following over the past couple weeks. They have the same father, 4-year-old Luke, and their mothers, Shera and Nababiep, are sisters.
The lion cub webcam now toggles between four different views, so that you can view both litters of cubs, either playing outside or still snuggling with their mother.
Video: New lion cubs with mother Nababiep shortly after birth, September 22./ Smithsonian National Zoo.
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Posted: 24 Sep 2010 09:22 AM PDT

By Duncan Geere, Wired UK
Many estimates of air pollution in developing countries are innaccurate, as there's no network of surface-based sensors that can find the worst-polluted areas. Scientists regularly have to rely on a few dated observations of questionable veracity.
However, Nasa has just published the first long-term global map that shows density of particulate matter below 2.5 micrometres in diameter. This size is important, because it's small enough to get past the body's defences and accumulate in the lungs, making it dangerous to human health. Epidemologists believe that they cause millions of premature deaths each year.
Satellites can't easily scan the surface of the Earth — they instead scan a column of air in the atmosphere, and the difficulty comes in getting readings at a particular level out of that data. The team who produced the map, Aaron van Donkelaar and Randall Martin at Dalhousie University, in Halifax in Nova Scotia, Canada, blended total-column aerosol measurements from satellites with information about how aerosols are distributed vertically in the atmosphere to obtain the data.
The map, as you can see above, shows a wide band of very high concentrations of particulate matter across the Sahara, Middle East, Central Asia and China, only interrupted by the Himalayas. Central Europe also shows a spike, including the south-east corner of England, and urban areas in North and South America stand out too.

The World Health Organisation's recommended level is 10 micrograms per cubic metre, so anything on the map that's green or above is cause for concern. Once in the lungs, the particles can cause asthma, cardiovascular diseases and bronchitis. Some very fine particles can even get into the bloodstream.
Some of the particulate matter is man-made and some is natural, and scientists haven't quite worked out the relative quantities yet, but both are dangerous to human health. In the Arabian and Sahara deserts, its mostly natural mineral dust lifted by the wind, but in eastern China and Northern India, it's more likely to be soot particles emitted by power plants, factories and cars.
The next step is to try and verify some of these measurements by expanding the ground-based network of sensors, with the eventual goal of finding out how long-term exposure to these particles affects human health on large scales.
"We can see clearly that a tremendous number of people are exposed to high levels of particulates", said Martin. "So far, nobody has looked at what that means in terms of mortality and disease."
Image: NASA
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Posted: 24 Sep 2010 07:26 AM PDT

Three hurricanes — Julia, Igor and Karl — look oddly serene in this footage taken from the International Space Station on September 16.
The video is almost 15 minutes long, but it's worth it. It opens on Hurricane Julia at about 7:45 am EDT from 225 miles above the Earth. Julia has since calmed down, but as it moved across the eastern Atlantic it was a raging Category 2 hurricane, with winds of 105 miles per hour.
Hurricane strengths are measured on the Saffir-Simpson Hurricane Scale, which goes from 1 ("Very dangerous winds will produce some damage") to 5 ("Catastrophic damage will occur").
At around 3:15 the view switches to Hurricane Igor, filmed at 9:15 am EDT. Igor was a Category 4 storm with 145 mile per hour winds, and swirled out to cover almost the entire visible slice of the planet. A different camera catches Igor from another angle starting at about 9:10.
A third storm takes focus around 11:42. The space station's cameras caught what was then Tropical Storm Karl at about 10:45 am EDT. Karl since crossed the Yucatan Peninsula overnight and grew into a Category 1 hurricane over the Bay of Campeche with winds of 75 miles an hour.
Seeing these huge storms slide past in a few minutes gives a striking sense of how quickly the International Space Station moves — it zips around Earth once every 90 minutes at about 17,500 miles per hour.
Video: NASA
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Posted: 24 Sep 2010 07:22 AM PDT

By Kate Shaw, Ars Technica
Mnemiopsis leidyi, a comb jelly, doesn't seem like a very formidable predator: it lacks good vision, isn't capable of sensing nearby food via mechanoreception, and can't move quickly enough to strike at prey. Its common name, "the sea walnut," certainly doesn't strike fear into the hearts of men. However, M. leidyi is an extremely effective stealth predator. A new paper in the Proceedings of the National Academy of Sciences this week details how this seemingly innocuous sea creature can be such a successful hunter.
The researchers used 2D digital particle image velocimetry, or DPIV, to study water movement around feeding M. leidyi. During this process, the water is seeded with particles which are then illuminated with a laser. The movement of these particles can be analyzed to visualize the velocity, direction, and movement patterns of the fluid.
DPIV revealed that M. leidyi use millions of cilia to move water and create feeding currents that trap nearby prey and carry it to their mouth. This technique isn't unique among animals; many bivalves and bryozoans use the same strategy. What makes this comb jelly's strategy different is its ability to create a laminar feeding current that is completely undetectable to the prey that's caught in the flow.

The currents created by other animals, such as oysters and mussels, have very high fluid deformation rates, meaning that the disturbance in the water can alert the prey to the presence of danger and give it the chance to escape. In contrast, the feeding currents created by M. leidyi have extraordinarily low deformation rates that are well below the detection thresholds of their prey.
Thanks to the slow speed of the current and the morphology of the comb jelly's mouth, the prey remains blissfully unaware of the impending danger until it is too late: the fluid deformation rates only exceed the prey's detection threshold once it has entered M. leidyi's critical capture zone. There, sticky tentillae in the comb jelly's mouth capture the prey with a near 100 percent success rate.
With this clever strategy, M. leidyi can feed at the same rate as many higher-level copepods and predatory fish (and possibly an even faster rate, according to less conservative estimates). Moreover, the hydrodynamically silent feeding current is capable of entraining a large variety of prey, including small copepods and even some fish larvae. Despite belonging to a basal lineage and lacking many of the attributes of many higher-order predators, the sea walnut's manipulation of fluid dynamics makes it a master stealth predator.
Source Link: Ars Technica
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Posted: 24 Sep 2010 07:07 AM PDT

By Mark Brown, Wired UK
Like many innovations in engineering, a newly developed matrix of sensors, designed to wrap round aircraft, takes much of its inspiration from the natural world. The device is influenced in shape by spiderwebs, and in purpose by birds.
Scientists at Stanford University say that while planes share many senses with birds — replacing eyes with radar and mouths with radio — they don't have a nervous system to track microscopic changes in their bodies. A bird's nerves and tissues allows the animal to sense whether a dive is putting its body under too much strain, for example, and pull up before hurting itself.
The scientists wanted to bring those senses to an airplane, so they created a cobweb-style matrix of sensors, which stretches around an aircraft and is used to detect strain and temperature. It will hook up to the aircraft's computer and allow a pilot to be aware of any tiny cracks or damages in the plane's body, or detect excess air pressure impacting one part of the craft, before they develop into life-threatening problems.
Its future implementation, the Standard researchers claim, will help ensure a much greater level of safety in air transportation.

The system is made up of lightweight sensors, to avoid adding significant weight to aircraft, laid out on top of a plastic polymer sheet. At first, the sheet is very small and doesn't look like a cobweb. That's until it's stretched out and expanded to more than 265 times its original size, where the strong, durable and almost invisible mesh of wires looks like a giant technological cobweb.
Stanford University scientist Fu-Kuo Chang says just one square foot of the sensor-equipped material could stretch far enough to cover an entire car. Plus, the technology will have implications that stretch further than the airline business. It could lead to smarter cars with similar awareness to external forces and internal measures, and wound dressings that tell doctors how far along the healing process is. Mixed with ultra-sonic sonar technology, the university even claims that pregnant women could wear shirts that show off their unborn child. Very creepy.
Other technology which owe their inspiration to the world of biology include Standford University's own Gecko toe-influenced climbing robots, NASA's honey bee-styled self-sacrificing spaceship swarms and General Electric's sensors based on butterfly wings.
Image: Flickr/Tyron Francis
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Posted: 24 Sep 2010 04:00 AM PDT
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The next Mars rover is only about a year away from taking off, and it's already stretching its arms and spinning its wheels in a lab in California. But scientists are still debating exactly where to drop it.
Curiosity (or more formally, the Mars Science Laboratory) is slated to launch in late 2011, and its chief objective is looking for life. That means landing in a spot where the soils formed in water, and where rocks could have preserved chemical traces of living organisms.
Now, after four years of deliberation, the rover crew has narrowed the choice down to their four favorites: a rugged valley full of water-bearing clays; and three craters that may once have been basins, lakes or river deltas. Hundreds of planetary scientists will descend on Monrovia, California, next week to continue the debate.
Image: NASA
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Posted: 23 Sep 2010 06:32 PM PDT

Exploring the peculiar effects of Einstein's relativity is no longer rocket science. Tabletop experiments at a lab in Colorado have illustrated the odd behavior of time, a strangeness typically probed with space travel and jet planes.
sciencenewsUsing superprecise atomic clocks, scientists have witnessed time dilation — the bizarre speeding up or slowing down of time described by Einstein's theories of relativity. The experiments are presented in the Sept. 24 Science.
"Modern technology has gotten so precise you can see these exotic effects in the range of your living room," says physicist Clifford Will of Washington University in St. Louis. The experiments don't reveal any new physics, Will says, but "what makes it cute and pretty cool is they have done it on a tabletop."
Time dilation arises in two situations. In one case, time appears to move slower the closer you are to a massive object, such as the Earth. So a person hovering in a hot-air balloon, for example, actually ages faster than someone standing below.
Time also ticks by faster for someone at rest relative to someone moving. Einstein dramatized this second strangeness with the twin paradox — one 25-year-old twin traveling in a rocket ship near the speed of light for what he perceives as a few months will return to Earth to find the other has reached middle age.
Previous experiments with rockets and airplanes have demonstrated these odd aspects of general and special relativity. The notion of time running slower closer to Earth was even tested on the scale of a multistory physics building at Harvard.
Now advances in laser technology and the field of quantum information science have allowed researchers to demonstrate Einstein's theories at much more ordinary scales.
The researchers used two optical atomic clocks sitting atop steel tables in neighboring labs at the National Institute of Standards and Technology in Boulder, Colorado. Each clock has an electrically charged aluminum atom, or ion, that vibrates between two energy levels more than a million billion times per second. A 75-meter-long optical cable connects the clocks, which allows the team to compare the instruments' timekeeping.
In the first experiment, physicist James Chin-wen Chou and his colleagues at NIST used a hydraulic jack to raise one of the tables 33 centimeters, or about a foot. Sure enough, the lower clock ran slower than the elevated one — at the rate of a 90-billionth of a second in 79 years. In a second experiment the team applied an electric field to one clock, sending the aluminum ion moving back and forth. As predicted, the moving clock ran slower than the clock that was at rest.
"It's pretty breathtaking precision," says physicist Daniel Kleppner of MIT. Of course scientists are well aware of these relativistic effects, he notes. The clocks on GPS devices are also affected by relativity, and appropriate adjustments are made to keep them working properly.
The experiments have more implications for precision instrumentation than they do for relativity, notes Chou. But they are a nice reminder that relativity is always at hand. "People tend to just ignore relativistic effects, but relativistic effects are everywhere," he says. "Every day, people are moving; they are doing things like climbing stairs. It's interesting to think about — are frequent flyers getting younger [because they move so much] or aging faster [because they spend so much time in the air]?"
Image: AAAS/Science
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Posted: 23 Sep 2010 05:05 PM PDT

A hole in the dust disk surrounding our solar system would tell alien observers there are planets here, a new simulation shows. The new model, which tracks thousands of tiny particles beyond the orbit of Neptune, could help astronomers work out the properties of planets in other stars' dust disks.
"We're trying to create a new planet-search technique, and we're practicing on the solar system," said NASA exoplanet scientist Marc Kuchner, lead author of a paper describing the results in the Sept. 7 Astrophysical Journal.
The cloud of dust comes from the Kuiper belt, the region beyond Neptune that contains small, icy bodies, including Pluto. These giant snowballs sometimes smack into each other, sending up flurries of ice grains. These tiny clots of ice and minerals get tugged around by the gravitational influence of giant planets, as well as the solar wind and small nudges from sunlight.
Similar clouds of dust has been spotted around several other stars, including Fomalhaut, the first star to have its planets directly photographed. Most extrasolar planets are too dim to have their portraits taken directly, but their presence can warp the disk of dust and debris around their stars into distinctive shapes, telling outside observers that planets are there.

Kuchner and co-author Christopher Stark of the University of Maryland wondered how much information these dust clouds can offer.
"This field of studying shapes of debris disks has been around for a while, but it's been qualitative," Kuchner said. "We're trying to make it quantitative. We want to get to where you can give us a picture of a debris disk, and we can say bam — here are the planets, and here's how massive they are."
The researchers used a supercomputer at NASA's Goddard Spaceflight Center to simulate 75,000 particles bumping around the Kuiper belt. Their model is the first to include not just collisions between Pluto-sized bodies, but the tiny dust grains as well.
"You have something like a billion billion million particles, and they're all hitting each other," Kuchner said. "Nobody before had figured out how to keep track of all that stuff."
Rather than directly tracking all those particles, Kuchner's model looked at two separate pictures: how the particles moved without collisions, and the density and velocity of the particles. The model then integrated the two pictures to paint a fuller portrait of the dusty disk.
The results showed that a hole in the dust follows Neptune around in its orbit. Neptune's gravity traps some of the dust grains in a gravitational tango called a resonance, which pulls the dust into clumps that precede and follow the gas giant around the sun. Earlier studies have shown that the Earth does the same thing with dust released from the asteroid belt.
"When you have low dust levels, like in today's solar system, dust moves into resonances and makes a gap, which tells you where Neptune is," Kuchner said.
When the fragile dust grains collide, they can annihilate each other, he said. In today's wide, fuzzy Kuiper belt, the particles don't meet very often, so they stick around long enough to fall into resonances with Neptune. But earlier in the solar system's history — and in planetary systems around other stars like Fomalhaut — the dust grains are destroyed before they have a chance to wander away from where they were created.
Kuchner tweaked his model to simulate the solar system at 700 million, 100 million and 15 million years old. As he turned back the clock, the dust disk collapsed into a dense, bright ring.
"Our models of this ring let us sort of look back in time to when the solar system was young," said Marc Kuchner. "When we do that we find that this ring looks just like the rings we see around other stars, like Fomalhaut."
The model has some shortcomings. For one thing, it ignores grains smaller than a certain threshold, which could be important for creating dust. Also, astronomers don't have a very clear picture of what the Kuiper belt contains, so the model's input parameters could be off.
Still, the model is a welcome addition to other Kuiper-belt researchers. "I'm happy to see another well-studied Kuiper-belt–dust paper in the community. We need it," said astronomer Amara Graps of the Southwest Research Institute in Boulder, Colorado. "The dusty byproduct of those small bodies is still not well-understood, and I believe that Marc made an important contribution."

Images: 1) NASA/Goddard/Marc Kuchner and Christopher Stark 2) NASA/ESA/P. Kalas (Univ. of California, Berkeley) et al.
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