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'Cool' Gas May Form and Strengthen Sunspots

Science Daily  -  Hydrogen molecules may act as a kind of energy sink that strengthens the magnetic grip that causes sunspots, according to scientists from Hawaii and New Mexico using a new infrared instrument on an old telescope.

"We think that molecular hydrogen plays an important role in the formation and evolution of sunspots," said Dr. Sarah Jaeggli, a recent University of Hawaii at Manoa graduate whose doctoral research formed a key element of the new findings. She conducted the research with Drs. Haosheng Lin, also from the University of Hawaii at Manoa, and Han Uitenbroek of the National Solar Observatory in Sunspot, NM. Jaeggli now is a postdoctoral researcher in the solar group at Montana State University. Their work is published in the Feb. 1, 2012, issue of The Astrophysical Journal.

They used the new Facility Infrared Spectropolarimeter (FIRS; Seeing Red, below) at the Dunn Solar Telescope at Sunspot, NM, and the older Horizontal Spectrograph. Although built in 1969, the Dunn now is equipped with advanced adaptive optics that correct for much of atmospheric blurring.

The team analyzed seven active regions on the Sun, one in 2001 and six during December 2010 to December 2011 as Sunspot Cycle 23 faded away. The full sunspot sample has 56 observations of 23 different active regions.

Sunspots appear to come and go in approximate 11-year cycles. They are brighter than an arc-welder's torch, but appear black because the surrounding solar surface is so much brighter. Galileo and his contemporaries discovered sunspots in 1610. George Ellery Hale discovered magnetism in spots in 1908, and scientists soon determined that intense magnetism suppresses the normal convective motions present throughout the solar photosphere and forms "cool" spots.

But the details remain a mystery. Among the clues solar physicists have observed is a direct relationship between the spot's inner temperature and its magnetic field strength. But at very low temperatures, the field strength makes a sharp rise.

"This result is puzzling," Jaeggli and her colleagues wrote. It implies some undiscovered mechanism inside the spot.

One suspect is hydrogen atoms combining into hydrogen molecules (H2). The Sun is about 90 percent hydrogen atoms (plus 10 percent helium and 0.13 percent everything else). Most of the hydrogen is ionized atoms since the average surface temperature is an inferno-like 5780K (9944 deg. F). Yet it is a "cool star" since astronomers can detect heavy-element molecules in the solar spectrum. In 1997 they even found water, as traces of super-heated steam, inside spots.

This suggests that a spot's cool umbra, the "black" shadow at center, might let hydrogen molecules combine in surface layers. As early as 1986 the late Prof. Per E. Maltby and colleagues at the University of Oslo predicted that the gas in the umbra could be as much as 5 percent hydrogen molecules.

Such a shift would cause a major change in sunspot dynamics. A basic law of physics is that gas particles exert the same pressure whether they are atoms or molecules. A hydrogen molecule will provide half the pressure of the two atoms it used to be. And bonds between atoms oscillate and rotate, thus storing energy without raising the temperature. (This is why water absorbs a lot of heat before boiling.)

"The formation of a large fraction of molecules may have important effects on the thermodynamic properties of the solar atmosphere and the physics of sunspots," Jaeggli wrote.

But direct measurement of hydrogen molecules in spots is beyond our grasp for now, so the team measured a stand-in, the hydroxyl radical made of one atom each of hydrogen and oxygen (OH). About 1 percent of the mass of the Sun is oxygen. OH dissociates (breaks into atoms) at a slightly lower temperature than H2, meaning H2 can also form in regions where OH is present. By coincidence, one of its infrared spectral lines is 1565.2nm, almost the same as the 1565nm line of iron, used for measuring magnetism in a spot and one of the lines FIRS is designed to observe. (These are twice the wavelength of the deepest red, 770nm, the human eye can see.)

First using the older HSG in 2001, and then with the more advanced FIRS in 2009-10, the team measured magnetic fields across sunspots, and the OH intensity inside spots. From that, they calculated the H2 concentrations.

"We found evidence that significant quantities of hydrogen molecules form in sunspots that are able to maintain magnetic fields stronger than 2,500 Gauss," Jaeggli said. By comparison, Earth's magnetic field, which turns a compass needle, is about one-half Gauss. The team estimated a hydrogen molecule quantity of a few percent.

Jaeggli said its presence leads to a temporary "runaway" intensification of the magnetic field. Magnetic flux emerges from the interior and suppresses convection at the surface, trapping cool gas that has radiated its energy into space. Molecular hydrogen forms, reducing the volume. This is more transparent than atomic hydrogen, so more energy radiates into space, cooling the gas further. Hot gases around the emerging flux compress the cooler region and intensify the magnetic field.

Eventually it levels out, partly from energy radiating in from the surrounding gas. Otherwise, the spot would grow without bounds. As the magnetic field weakens, the H2 and OH molecules heat up and dissociate back to atoms, compressing the remaining cool regions and keeping the spot from collapsing.

The team says that simulations are needed to test their observations. They also note that most of the active regions observed are of modest field strength. They expect that Cycle 24, which is now ramping up, will provide stronger active regions for a test of their hypothesis.

NSO's mission is to advance knowledge of the Sun, both as an astronomical object and as the dominant external influence on Earth, by providing forefront observational opportunities to the research community. NSO is operated by Association of Universities for Research in Astronomy (AURA Inc.) under a cooperative agreement with the National Science Foundation (NSF) for the benefit of the astronomical community.

Founded in 1967, the Institute for Astronomy at the University of Hawaii at Manoa conducts research into galaxies, cosmology, stars, planets, and the Sun. Its faculty and staff are also involved in astronomy education, deep space missions, and in the development and management of the observatories on Haleakala and Mauna Kea.

Seeing Red

The Facility Infrared Spectropolarimeter (FIRS) at the National Solar Observatory's Dunn Solar Telescope is an advanced imaging spectropolarimeter developed by Haosheng Lin and colleagues at the Institute for Astronomy, University of Hawaii at Manoa, and NSO.

FIRS provides simultaneous spectral coverage at visible and infrared wavelengths through the use of a unique dual-armed spectrograph. The geometry of the spectrograph has been specially designed to capture 630.2nm and 1564.8nm lines of hot, neutral iron (Fe I) with maximum efficiency. It can be re-tuned so the infrared arm instead captures light from helium or silicon around 1083nm or, for this study, OH at 1565nm.

In addition, the spectrograph operates in a multiple slit mode. By using narrowband filters, the spectra from four consecutive slit positions can be imaged at once on the same detector. This feature decreases fourfold the time necessary to scan across a large area on the sun, making it an ideal instrument for the study of quickly developing active regions as illustrated in this "data cube" movie. It also operates simultaneously with other instruments at the Dunn, making for powerful observational capabilities.

The thinness of graphene enables near-perfect wetting transparency

Science Daily  -  Graphene is the thinnest material known to science. The nanomaterial is so thin, in fact, water often doesn't even know it's there.

Engineering researchers at Rensselaer Polytechnic Institute and Rice University coated pieces of gold, copper, and silicon with a single layer of graphene, and then placed a drop of water on the coated surfaces. Surprisingly, the layer of graphene proved to have virtually no impact on the manner in which water spreads on the surfaces.

Results of the study were published in the journal Nature Materials. The findings could help inform a new generation of graphene-based flexible electronic devices. Additionally, the research suggests a new type of heat pipe that uses graphene-coated copper to cool computer chips.

The discovery stemmed from a cross-university collaboration led by Rensselaer Professor Nikhil Koratkar and Rice Professor Pulickel Ajayan.

"We coated several different surfaces with graphene, and then put a drop of water on them to see what would happen. What we saw was a big surprise -- nothing changed. The graphene was completely transparent to the water," said Koratkar, a faculty member in the Department of Mechanical, Aerospace, and Nuclear Engineering and the Department of Materials Science and Engineering at Rensselaer. "The single layer of graphene was so thin that it did not significantly disrupt the non-bonding van der Waals forces that control the interaction of water with the solid surface. It's an exciting discovery, and is another example of the unique and extraordinary characteristics of graphene."

Results of the study are detailed in the Nature Materials paper "Wetting transparency of graphene."

Essentially an isolated layer of the graphite found commonly in our pencils or the charcoal we burn on our barbeques, graphene is single layer of carbon atoms arranged like a nanoscale chicken-wire fence. Graphene is known to have excellent mechanical properties. The material is strong and tough and because of its flexibility can evenly coat nearly any surface. Many researchers and technology leaders see graphene as an enabling material that could greatly advance the advent of flexible, paper-thin devices and displays. Used as a coating for such devices, the graphene would certainly come into contact with moisture. Understanding how graphene interacts with moisture was the impetus behind this new study.

The spreading of water on a solid surface is called wetting. Calculating wettability involves placing a drop of water on a surface, and then measuring the angle at which the droplet meets the surface. The droplet will ball up and have a high contact angle on a hydrophobic surface. Inversely, the droplet will spread out and have a low contact angle on a hydrophilic surface.

The contact angle of gold is about 77 degrees. Koratkar and Ajayan found that after coating a gold surface with a single layer of graphene, the contact angle became about 78 degrees. Similarly, the contact angle of silicon rose from roughly 32 degrees to roughly 33 degrees, and copper increased from around 85 degrees to around 86 degrees, after adding a layer of graphene.

These results surprised the researchers. Graphene is impermeable, as the tiny spaces between its linked carbon atoms are too small for water, or a single proton, or anything else to fit through. Because of this, one would expect that water would not act as if it were on gold, silicon, or copper, since the graphene coating prevents the water from directly contacting these surfaces. But the research findings clearly show how the water is able to sense the presence of the underlying surface, and spreads on those surfaces as if the graphene were not present at all.

As the researchers increased the number of layers of graphene, however, it became less transparent to the water and the contact angles jumped significantly. After adding six layers of graphene, the water no longer saw the gold, copper, or silicon and instead behaved as if it was sitting on graphite.

The reason for this perplexing behavior is subtle. Water forms chemical or hydrogen bonds with certain surfaces, while the attraction of water to other surfaces is dictated by non-bonding interactions called van der Waals forces. These non-bonding forces are not unlike a nanoscale version of gravity, Koratkar said. Similar to how gravity dictates the interaction between Earth and the sun, van der Waals forces dictate the interaction between atoms and molecules.

In the case of gold, copper, silicon, and other materials, the van der Waals forces between the surface and water droplet determine the attraction of water to the surface and dictate how water spreads on the solid surface. In general, these forces have a range of at least several nanometers. Because of the long range, these forces are not disrupted by the presence of a single-atom-thick layer of graphene between the surface and the water. In other words, the van der Waals forces are able to "look through" ultra-thin graphene coatings, Koratkar said.

If you continue to add additional layers of graphene, however, the van der Waals forces increasingly "see" the carbon coating on top of the material instead of the underlying surface material. After stacking six layers of graphene, the separation between the graphene and the surface is sufficiently large to ensure that the van der Waals forces can now no longer sense the presence of the underlying surface and instead only see the graphene coating. On surfaces where water forms hydrogen bonds with the surface, the wetting transparency effect described above does not hold because such chemical bonds cannot form through the graphene layer.

Along with conducting physical experiments, the researchers verified their findings with molecular dynamics modeling as well as classical theoretical modeling.

"We found that van der Waals forces are not disrupted by graphene. This effect is an artifact of the extreme thinness of graphene -- which is only about 0.3 nanometers thick," Koratkar said. "Nothing can rival the thinness of graphene. Because of this, graphene is the ideal material for wetting angle transparency."

"Moreover, graphene is strong and flexible, and it does not easily crack or break apart," he said. "Additionally, it is easy to coat a surface with graphene using chemical vapor deposition, and it is relatively uncomplicated to deposit uniform and homogeneous graphene coatings over large areas. Finally, graphene is chemically inert, which means a graphene coating will not oxidize away. No single material system can provide all of the above attributes that graphene is able to offer."

A practical application of this new discovery is to coat copper surfaces used in dehumidifiers. Because of its exposure to water, copper in dehumidifier systems oxidizes, which in turn decreases its ability to transfer heat and makes the entire device less efficient. Coating the copper with graphene prevents oxidation, the researchers said, and the operation of the device is unaffected because graphene does not change the way water interacts with copper. This same concept may be applied to improve the ability of heat pipes to dissipate heat from computer chips, Koratkar said.

"It's an interesting idea. The graphene doesn't cause any significant change to the wettability of copper, and at the same time it passivates the copper surface and prevents it from oxidizing," he said.

Almost Perfect: Researcher Nears Creation of Superlens

Science Daily  -  A superlens would let you see a virus in a drop of blood and open the door to better and cheaper electronics. It might, says Durdu Guney, make ultra-high-resolution microscopes as commonplace as cameras in our cell phones.

No one has yet made a superlens, also known as a perfect lens, though people are trying. Optical lenses are limited by the nature of light, the so-called diffraction limit, so even the best won't usually let us see objects smaller than 200 nanometers across, about the size of the smallest bacterium. Scanning electron microscopes can capture objects that are much smaller, about a nanometer wide, but they are expensive, heavy, and, at the size of a large desk, not very portable.

To build a superlens, you need metamaterials: artificial materials with properties not seen in nature. Scientists are beginning to fabricate metamaterials in their quest to make real seemingly magical phenomena like invisibility cloaks, quantum levitation -- and superlenses.

Now Guney, an assistant professor of electrical and computer engineering at Michigan Technological University, has taken a major step toward creating superlens that could use visible light to see objects as small as 100 nanometers across.

The secret lies in plasmons, charge oscillations near the surface of thin metal films that combine with special nanostructures. When excited by an electromagnetic field, they gather light waves from an object and refract it in a way not seen in nature called negative refraction. This lets the lens overcomes the diffraction limit. And, in the case of Guney's model, it could allow us to see objects smaller than 1/1,000th the width of a human hair.

Other researchers have also been able to sidestep the diffraction limit, but not throughout the entire spectrum of visible light. Guney's model showed how metamaterials might be "stretched" to refract light waves from the infrared all the way past visible light and into the ultraviolet spectrum.

Making these superlenses would be relatively inexpensive, which is why they might find their way into cell phones. But there would be other uses as well, says Guney.

"It could also be applied to lithography," the microfabrication process used in electronics manufacturing. "The lens determines the feature size you can make, and by replacing an old lens with this superlens, you could make smaller features at a lower cost. You could make devices as small as you like."

Computer chips are made using UV lasers, which are expensive and difficult to build. "With this superlens, you could use a red laser, like the pointers everyone uses, and have simple, cheap machines, just by changing the lens."

What excites Guney the most, however, is that a cheap, accessible superlens could open our collective eyes to worlds previously known only to a very few.

"The public's access to high-powered microscopes is negligible," he says. "With superlenses, everybody could be a scientist. People could put their cells on Facebook. It might just inspire society's scientific soul."

Researchers Cloak a Moment in Time

Science Daily  -  Think Harry Potter movie magic: Cornell researchers have demonstrated a "temporal cloak" -- albeit on a very small scale -- in the transport of information by a beam of light.

The trick is to create a gap in the beam of light, have the hidden event occur as the gap goes by and then stitch the beam back together. Alexander Gaeta, Cornell professor of applied and engineering physics, and colleagues report their work entitled "Demonstration of temporal cloaking," in the journal Nature (Jan. 5, 2012.)

The researchers created what they call a time lens, which can manipulate and focus signals in time, analogous to the way a glass lens focuses light in space. They use a technique called four-wave mixing, in which two beams of light, a "signal" and a "pump," are sent together through an optical fiber. The two beams interact and change the wavelength of the signal. To begin creating a time gap, the researchers first bump the wavelength of the signal up, then by flipping the wavelength of the pump beam, bump it down.

The beam then passes through another, very long, stretch of optical fiber. Light passing through a transparent material is slowed down just a bit, and how much it is slowed varies with the wavelength. So the lower wavelength pulls ahead of the higher, leaving a gap, like the hare pulling ahead of the tortoise. During the gap the experimenters introduced a brief flash of light at a still higher wavelength that would cause a glitch in the beam coming out the other end.

Then the split beam passes through more optical fiber with a different composition, engineered to slow lower wavelengths more than higher. The higher wavelength signal now catches up with the lower, closing the gap. The hare is plodding through mud, but the tortoise is good at that and catches up. Finally, another four-wave mixer brings both parts back to the original wavelength, and the beam emerges with no trace that there ever was a gap, and no evidence of the intruding signal.

None of this will let you steal the crown jewels without anyone noticing. The gap created in the experiment was 15 picoseconds long, and might be increased up to 10 nanoseconds, Gaeta said. But the technique could have applications in fiber-optic data transmission and data processing, he added. For example, it might allow inserting an emergency signal without interrupting the main data stream, or multitasking operations in a photonic computer, where light beams on a chip replace wires.

The experiment was inspired by a theoretical proposal for a space-time cloak or "history editor" published by Martin McCall, professor of physics at Imperial College in London, in the Journal of Optics in November 2010. "But his method required an optical response from a material that does not exist. Now we've done it in one spatial dimension. Extending it to two [that is, hiding a moment in an entire scene] is not out of the realm of possibility. All advances have to start from somewhere," Gaeta says.

Discoveries

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Science decodes 'internal voices'

Researchers have demonstrated a striking method to reconstruct words, based on the brain waves of patients thinking of those words.

The technique reported in PLoS Biology relies on gathering electrical signals directly from patients' brains.

Based on signals from listening patients, a computer model was used to reconstruct the sounds of words that patients were thinking of.

The method may in future help comatose and locked-in patients communicate.

Several approaches have in recent years suggested that scientists are closing in on methods to tap into our very thoughts; the current study achieved its result by implanting electrodes directly into a part of participants' brains.

In a 2011 study, participants with electrodes in direct brain contact were able to move a cursor on a screen by simply thinking of vowel sounds.

A technique called functional magnetic resonance imaging to track blood flow in the brain has shown promise for identifying which words or ideas someone may be thinking about.

By studying patterns of blood flow related to particular images, Jack Gallant's group at the University of California Berkeley showed in September that patterns can be used to guess images being thought of - recreating "movies in the mind".

Now, Brian Pasley of the University of California, Berkeley and a team of colleagues have taken that "stimulus reconstruction" work one step further.

"This is inspired by a lot of Jack's work," Dr Pasley said. "One question was... how far can we get in the auditory system by taking a very similar modeling approach?"

The team focused on an area of the brain called the superior temporal gyrus, or STG.

This broad region is not just part of the hearing apparatus but one of the "higher-order" brain regions that help us make linguistic sense of the sounds we hear.

The team monitored the STG brain waves of 15 patients who were undergoing surgery for epilepsy or tumors, while playing audio of a number of different speakers reciting words and sentences.

The trick is disentangling the chaos of electrical signals that the audio brought about in the patients' STG regions.

To do that, the team employed a computer model that helped map out which parts of the brain were firing at what rate, when different frequencies of sound were played.

With the help of that model, when patients were presented with words to think about, the team was able to guess which word the participants had chosen.

They were even able to reconstruct some of the words, turning the brain waves they saw back into sound on the basis of what the computer model suggested those waves meant.

"There's a two-pronged nature of this work - one is the basic science of how the brain does things," said Robert Knight of UC Berkeley, senior author of the study.

"From a prosthetic view, people who have speech disorders... could possibly have a prosthetic device when they can't speak but they can imagine what they want to say," Prof Knight explained.

"The patients are giving us this data, so it'd be nice if we gave something back to them eventually."

The authors caution that the thought-translation idea is still to be vastly improved before such prosthetics become a reality.

But the benefits of such devices could be transformative, said Mindy McCumber, a speech-language pathologist at Florida Hospital in Orlando.

"As a therapist, I can see potential implications for the restoration of communication for a wide range of disorders," she told BBC News.

"The development of direct neuro-control over virtual or physical devices would revolutionize 'augmentative and alternative communication', and improve quality of life immensely for those who suffer from impaired communication skills or means."

Revisiting the 'Pillars of Creation'

In 1995, NASA's Hubble Space Telescope took an iconic image of the Eagle nebula, dubbed the "Pillars of Creation," highlighting its finger-like pillars where new stars are thought to be forming. Now, the Herschel Space Observatory has a new, expansive view of the region captured in longer-wavelength infrared light.

The Herschel mission is led by the European Space Agency, with important NASA contributions.

The Eagle nebula is 6,500 light-years away in the constellation of Serpens. It contains a young, hot star cluster, NGC6611, visible with modest backyard telescopes, which is sculpting and illuminating the surrounding gas and dust. The result is a huge, hollowed-out cavity and pillars, each several light-years long.

The new Herschel image shows the pillars and the wide field of gas and dust around them. Captured in far-infrared wavelengths, the image allows astronomers to see inside the pillars and structures in the region. Herschel's image also makes it possible to search for young stars over a much wider region, and come to a much fuller understanding of the creative and destructive forces inside the Eagle nebula.

Herschel is a European Space Agency cornerstone mission, with science instruments provided by consortia of European institutes and with important participation by NASA. NASA's Herschel Project Office is based at NASA's Jet Propulsion Laboratory, Pasadena, Calif. JPL contributed mission-enabling technology for two of Herschel's three science instruments. The NASA Herschel Science Center, part of the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena, supports the United States astronomical community. Caltech manages JPL for NASA.

More information is online at: http://www.herschel.caltech.edu and http://www.nasa.gov/herschel  .

Electron's negativity cut in half by supercomputer: simulations slice electron in half — a physical process that can't be done in nature

While physicists at the Large Hadron Collider smash together thousands of protons and other particles to see what matter is made of, they're never going to hurl electrons at each other. No matter how high the energy, the little negative particles won't break apart. But that doesn't mean they are indestructible.

Using several massive supercomputers, a team of physicists has split a simulated electron perfectly in half. The results, which were published in the Jan. 13 issue of Science, are another example of how tabletop experiments on ultra-cold atoms and other condensed-matter materials can provide clues about the behavior of fundamental particles.

In the simulations, Duke University physicist Matthew Hastings and his colleagues, Sergei Isakov of the University of Zurich and Roger Melko of the University of Waterloo in Canada, developed a virtual crystal. Under extremely low temperatures in the computer model, the crystal turned into a quantum fluid, an exotic state of matter where electrons begin to condense.

Many different types of materials, from superconductors to superfluids, can form as electrons condense and are chilled close to absolute zero, about -459 degrees Fahrenheit. That's approximately the temperature at which particles simply stop moving. It's also the temperature region where individual particles, such as electrons, can overcome their repulsion for each other and cooperate.

The cooperating particles' behavior eventually becomes indistinguishable from the actions of an individual. Hastings says the phenomenon is a lot like what happens with sound. A sound is made of sound waves. Each sound wave seems to be indivisible and to act a lot like a fundamental particle. But a sound wave is actually the collective motion of many atoms, he says.

Under ultra-cold conditions, electrons take on the same type of appearance. Their collective motion is just like the movement of an individual particle. But, unlike sound waves, cooperating electrons and other particles, called collective excitations or quasiparticles, can "do things that you wouldn't think possible," Hastings says.

The quasiparticles formed in this simulation show what happens if a fundamental particle were busted up, so an electron can't be physically smashed into anything smaller, but it can be broken up metaphorically, Hastings says.

He and his colleagues divided one up by placing a virtual particle with the fundamental charge of an electron into their simulated quantum fluid. Under the conditions, the particle fractured into two pieces, each of which took on one-half of the original's negative charge.

As the physicists continued to observe the new sub-particles and change the constraints of the simulated environment, they were also able to measure several universal numbers that characterize the motions of the electron fragments. The results provide scientists with information to look for signatures of electron pieces in other simulations, experiments and theoretical studies.

Successfully simulating an electron split also suggests that physicists don't necessarily have to smash matter open to see what's inside; instead, there could be other ways to coax a particle to reveal itself.