Flaky graphene makes reliable chemical sensors

Scientists from the University of Illinois at Urbana-Champaign and the company Dioxide Materials have demonstrated that randomly stacked graphene flakes can make an effective chemical sensor.

The researchers created the one-atom-thick carbon lattice flakes by placing bulk graphite in a solution and bombarding it with ultrasonic waves that broke off thin sheets. The researchers then filtered the solution to produce a graphene film, composed of a haphazard arrangement of stacked flakes, that they used as the top layer of a chemical sensor. When the graphene was exposed to test chemicals that altered the surface chemistry of the film, the subsequent movement of electrons through the film produced an electrical signal that flagged the presence of the chemical.

The researchers experimented by adjusting the volume of the filtered solution to make thicker or thinner films. They found that thin films of randomly stacked graphene could more reliably detect trace amounts of test chemicals than previously designed sensors made from carbon nanotubes or graphene crystals.

The results are accepted for publication in the AIP's journal Applied Physics Letters.

The researchers theorize that the improved sensitivity is due to the fact that defects in the carbon-lattice structure near the edge of the graphene flakes allow electrons to easily "hop" through the film.

NASA sees repeating La Niña hitting it's peak

La Niña, "the diva of drought," is peaking, increasing the odds that the Pacific Northwest will have more stormy weather this winter and spring, while the southwestern and southern United States will be dry.

Sea surface height data from NASA's Jason-1 and -2 satellites show that the milder repeat of last year's strong La Niña has recently intensified, as seen in the latest Jason-2 image of the Pacific Ocean.

The image is based on the average of 10 days of data centered on Jan. 8, 2012. It depicts places where the Pacific sea surface height is higher than normal (due to warm water) as yellow and red, while places where the sea surface is lower than normal (due to cool water) are shown in blues and purples. Green indicates near-normal conditions. The height of the sea surface over a given area is an indicator of ocean temperature and other factors that influence climate.

This is the second consecutive year that the Jason altimetric satellites have measured lower-than-normal sea surface heights in the equatorial Pacific and unusually high sea surface heights in the western Pacific.

"Conditions are ripe for a stormy, wet winter in the Pacific Northwest and a dry, relatively rainless winter in Southern California, the Southwest and the southern tier of the United States," says climatologist Bill Patzert of JPL. "After more than a decade of mostly dry years on the Colorado River watershed and in the American Southwest, and only two normal rain years in the past six years in Southern California, low water supplies are lurking. This La Niña could deepen the drought in the already parched Southwest and could also worsen conditions that have fueled recent deadly wildfires."

NASA will continue to monitor this latest La Niña to see whether it has reached its expected winter peak or continues to strengthen.

A repeat of La Niña ocean conditions from one year to the next is not uncommon: repeating La Niñas occurred most recently in 1973-74-75, 1998-99-2000 and in 2007-08-09. Repeating La Niñas most often follow an El Niño episode and are essentially the opposite of El Niño conditions. During a La Niña episode, trade winds are stronger than normal, and the cold water that normally exists along the coast of South America extends to the central equatorial Pacific.

La Niña episodes change global weather patterns and are associated with less moisture in the air over cooler ocean waters. This results in less rain along the coasts of North and South America and along the equator, and more rain in the far Western Pacific.

The comings and goings of El Niño and La Niña are part of a long-term, evolving state of global climate, for which measurements of sea surface height are a key indicator. Jason-1 is a joint effort between NASA and the French Space Agency, Centre National d'Études Spatiales (CNES). Jason-2 is a joint effort between NASA, the National Oceanic and Atmospheric Administration, CNES and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). JPL manages the U.S. portion of both missions for NASA's Science Mission Directorate, Washington, D.C.

For more on how La Niña and other climate phenomena are affecting weather in the United States this year, see: http://science.nasa.gov/science-news/science-at-nasa/2012/17jan_missingsnow/ .

For more information on NASA's ocean surface topography missions, visit: http://sealevel.jpl.nasa.gov/

Flexible adult stem cells, right there in zour eye

In the future, patients in need of perfectly matched neural stem cells may not need to look any further than their own eyes. Researchers reporting in the January issue of Cell Stem Cell, a Cell Press publication, have identified adult stem cells of the central nervous system in a single layer of cells at the back of the eye.

That cell layer, known as the retinal pigment epithelium (RPE), underlies and supports photoreceptors in the light-sensitive retina. Without it, photoreceptors and vision are lost. The new study shows that the RPE also harbors self-renewing stem cells that can wake up to produce actively growing cultures when placed under the right conditions. They can also be coaxed into forming other cell types.

"You can get these cells from a 99-year-old," said Sally Temple of the Neural Stem Cell Institute in Rensselaer, New York. "These cells are laid down in the embryo and can remain dormant for 100 years. Yet you can pull them out and put them in culture and they begin dividing. It is kind of mind boggling."

Temple's group got the RPE-derived stem cells they describe from the eyes of donors in the hours immediately after their deaths. But the cells can also be isolated from the fluid that surrounds the retina at the back of the eye, which means they are accessible in living people as well.

"You can literally go in and poke a needle in the eye and get these cells from the subretinal space," she says. "It sounds awful, but retinal surgeons do it every day." By comparison, access to most other neural stem cell populations would require major surgery.

Temple said they were curious about the proliferative potential of the RPE given that the tissue is known to be capable of regenerating entire retinas in salamanders. But that plasticity in adulthood had seemed to be lost in mice and chicks. Still, "given the evolutionary evidence, we thought it was worth revisiting," she said.

They placed RPE tissue taken from 22-year-old to 99-year-old cadavers into many culture conditions to see what they could make the cells do. They found one set of conditions that got the cells dividing. Not all of the RPE cells have this regenerative potential, but perhaps 10 percent of them do.

Further work showed that the cells are multipotent, which means that they can form different cell types, though the researchers admit there is more to do to fully explore the cells' differentiation capacity.

There are other implications as well. For example, these cells may explain diseases in which other tissue types show up in the eye. Their presence also suggests that there might be some way to stimulate controlled repair of the eye in the millions of people who suffer from age-related macular degeneration.

"I think it might be possible," Temple said.

Most distant dwarf galaxy detected

Scientists have long struggled to detect the dim dwarf galaxies that orbit our own galaxy. So it came as a surprise on Jan. 18 when a team of astronomers using Keck II telescope's adaptive optics has announced the discovery of a dwarf galaxy halfway across the universe.

The new dwarf galaxy found by MIT's Dr. Simona Vegetti and colleagues is a satellite of an elliptical galaxy almost 10 billion light-years away from Earth. The team detected it by studying how the massive elliptical galaxy, called JVAS B1938 + 666, serves as a gravitational lens for light from an even more distant galaxy directly behind it. Their discovery was published in the Jan. 18 online edition of the journal Nature.

Like all supermassive elliptical galaxies, JVAS B1938 + 666's gravity can deflect light passing by it. Often the light from a background galaxy gets deformed into an arc around the lens galaxy, and sometimes what's called an Einstein ring. In this case, the ring is formed mainly by two lensed images of the background galaxy. The size, shape and brightness of the Einstein ring depends on the distribution of mass throughout the foreground lensing galaxy.

Vegetti and her team obtained extra sharp near-infrared image of JVAS B1938 + 666 by using the 10-meter Keck II telescope and its adaptive optics system, which corrects for the blurring effects of Earth's atmosphere, and provides stunningly sharp images. With these data, they neatly determined the mass distribution of JVAS B1938 + 666 as well as the shape and brightness of the background galaxy.

The researchers used a sophisticated numerical technique to derive a model of the lens galaxy's mass, as well as to map any excess lens mass that could not be accounted for by the galaxy. What they found was an excess mass near the Einstein ring that they attributed to the presence of a satellite, or "dwarf," galaxy. Vegetti's team also used a separate analytical model to test the detected excess mass. They found that a satellite galaxy is indeed required to explain the data.

"This satellite galaxy is exciting because it was detected in the excess-mass map despite its low mass," commented Robert Schmidt of the Center for Astronomy at Heidelberg University, in a related Nature article. "A natural question to ask is whether the satellite galaxy can be observed directly rather than by its gravitational effect on the shape of a background object. With current instrumentation, the answer is no. The object is simply too distant to be imaged directly. But the message here is that it is possible to spot these elusive objects around distant lens galaxies without knowing where to look for them."

Galaxies like our own are believed to form over billions of years through the merging of many smaller galaxies. So it's expected that there should be many smaller dwarf galaxies buzzing around the Milky Way. However, very few of these tiny relic galaxies have been observed which has led astronomers to conclude that many of them must have very few stars or possibly may be made almost exclusively of dark matter.

Scientists theorize the existence of dark matter to explain observations that suggest there is far more mass in the universe than can be seen. However, because the particles that make up dark matter do not absorb or emit light, they have so far proven impossible to detect and identify. Computer modeling suggests that the Milky Way should have about 10,000 satellite dwarf galaxies, but only 30 have been observed.

"It could be that many of the satellite galaxies are made of dark matter, making them elusive to detect, or there may be a problem with the way we think galaxies form," says Vegetti.

In the new study, Vegetti worked with Prof. Leon Koopmans of the University of Groningen, Netherlands; Dr. David Lagattuta and Prof. Christopher Fassnacht of the University of California at Davis; Dr. Matthew Auger of the University of California at Santa Barbara; and Dr. John McKean of the Netherlands Institute for Radio Astronomy.

"The existence of this low-mass dark galaxy is just within the bounds we expect if the Universe is composed of dark matter which has a low temperature. However, further dark satellites will need to be found to confirm this conclusion," says Vegetti.

PHYSICISTS DEVELOP FIRST CONCLUSIVE TEST TO BETTER UNDERSTANDING HIGH-ENERGY PARTICLES CORRELATIONS

Researchers have devised a proposal for the first conclusive experimental test of a phenomenon known as 'Bell's nonlocality.' This test is designed to reveal correlations that are stronger than any classical correlations, and do so between high-energy particles that do not consist of ordinary matter and light. These results are relevant to the so-called 'CP violation' principle, which is used to explain the dominance of matter over antimatter.

These findings by Beatrix Hiesmayr, a theoretical physicist at the University of Vienna, and her colleagues, a team of quantum information theory specialists, particle physicists and nuclear physicists, have been published in The European Physical Journal C.

According to the famous Einstein-Podolsky-Rosen Gedanken-Experiment, two particles that are measured independently obey the principle of locality, implying that an external influence on the first particle, such as measurement, has no direct influence on the second -- in other words there is no "spooky action at distance," as Einstein would likely have described it.

In an experimental setup, however, measurement results for one particle revealed a correlated measurement result for the other particle. Initially, these correlations could only be explained by referring to hidden parameters. In 1964, John Bell found that so-called local realistic hidden parameter theories imply that the relations between these correlations could be experimentally tested through so-called Bell tests. Since then many experiments have proven that local, realistic hidden parameters cannot be used as an explanation for these correlations.

In this study, the authors have succeeded in devising a new Bell test, taking into account the decay property of high-energy particles systems, called kaon-antikaon systems. This procedure ensures that the test is conclusive -- a goal that has never before been achieved -- and simultaneously guarantees its experimental testability. Experimental testing requires equipment such as the KLOE detector at the accelerator facility DAPHNE in Italy.

Revealing "spooky action at distance" for kaon-antikaon pairs has fundamental implications for our understanding of such particles' correlations and could ultimately allow us to determine whether symmetries in particle physics and manifestations of particles correlations are linked.

What's taking ET so long to find us

Mathematically speaking, ET should have found us by now - if he exists - so we're being consciously avoided for some reason, a new study concludes.

"We're either alone, or they're out there and leave us alone," says Florida Gulf Coast University mathematician Thomas Hair.

Hair, who presented his research at the Mathematical Association of America in Boston earlier this month, based his approximation of what he considered to be extremely conservative estimates for how long it would take a society to muster up the resources and technological know-how to leave its home world and travel to another star.

Even at the relatively sedate pace of 1 per cent of light-speed, the aliens would arrive at their nearest neighbour star in about 500 years.

Figure another 500 years to build new ships, set out again, and so on and so on, and the calculations show that civilisations starting out from the oldest stars in our galaxy would have had epochs of time to reach us by now. So where are they?

"They've either passed us by, or they stay around their home star systems and contemplate their navels," says Hair.

There could be several reasons why we're not listed in the intergalactic version of Trip Advisor or Lonely Planet. Perhaps most important is that we don't have anything aliens need.

"Any ancient civilisation is probably not biological. They don't need a place like Earth. They don't need to come here and steal our water. There's plenty of it out in the outer solar system where the gravity is not so great and they can just take all they want," says Hair.

Or perhaps modern-day extraterrestrials are following routes laid out long ago, all of which bypass Earth, he adds.
Giving ourselves away

Whatever the reason we're being ignored, there is no chance ET, if he or she exists, does not know we are here, says Hair, pointing to telescopes, such as NASA's Kepler observatory, which can detect planets around other stars.

If humans living on a planet that is roughly 5 billion years old have technology like Kepler, an alien civilisation with another 10 million years of experience under its belt would have advanced much further, Hair maintains.

"I'm sure they'd be able to detect if this planet had life on it. Just the CFCs (chlorofluorocarbons) in our atmosphere would give us away," he says.

CFCs are compounds typically found in refrigerants and aerosol products that release chlorine atoms when exposed to ultraviolet light and erode Earth's ozone layer.
Rare, weird and boring

University of Minnesota physicist Woods Halley, who just published a book about the prospects of extraterrestrial life, says we don't know enough about how life got started on Earth to be able to recognise alien life, even if it were staring us in the face.

"I think there are three options," says Halley. "Life is rare, which I think has a reasonable probability of being correct. Life is weird: every time you run into it, it's extremely different from the last time you saw it. Life is dull, meaning you will find something that looks a lot like life on Earth and our problems (in detecting life) are technical.

"I've come to the view that they're all possible, but the preponderance of evidence most likely fits the first - we are rare," says Halley.

Worlds smallest magnetic data storage unit

Scientists from IBM and the German Center for Free-Electron Laser Science (CFEL) have built the world's smallest magnetic data storage unit. It uses just twelve atoms per bit, the basic unit of information, and squeezes a whole byte (8 bit) into as few as 96 atoms. A modern hard drive, for comparison, still needs more than half a billion atoms per byte.

The team presented their work in the journal Science on January 13, 2012. CFEL is a joint venture of the research centre Deutsches Elektronen-Synchrotron DESY in Hamburg, the Max-Planck-Society (MPG) and the University of Hamburg. "With CFEL the partners have established an innovative institution on the DESY campus, delivering top-level research across a broad spectrum of disciplines," says DESY research director Edgar Weckert.

The nanometre data storage unit was built atom by atom with the help of a scanning tunneling microscope (STM) at IBM's Almaden Research Center in San Jose, California. The researchers constructed regular patterns of iron atoms, aligning them in rows of six atoms each. Two rows are sufficient to store one bit. A byte correspondingly consists of eight pairs of atom rows. It uses only an area of 4 by 16 nanometres (a nanometre being a millionth of a millimetre). "This corresponds to a storage density that is a hundred times higher compared to a modern hard drive," explains Sebastian Loth of CFEL, lead author of the Science paper.

Data are written into and read out from the nano storage unit with the help of an STM. The pairs of atom rows have two possible magnetic states, representing the two values '0' and '1' of a classical bit. An electric pulse from the STM tip flips the magnetic configuration from one to the other. A weaker pulse allows to read out the configuration, although the nano magnets are currently only stable at a frosty temperature of minus 268 degrees Centigrade (5 Kelvin). "Our work goes far beyond current data storage technology," says Loth. The researchers expect arrays of some 200 atoms to be stable at room temperature. Still it will take some time before atomic magnets can be used in data storage.

For the first time, the researchers have managed to employ a special form of magnetism for data storage purposes, called antiferromagnetism. Different from ferromagnetism, which is used in conventional hard drives, the spins of neighbouring atoms within antiferromagnetic material are oppositely aligned, rendering the material magnetically neutral on a bulk level. This means that antiferromagnetic atom rows can be spaced much more closely without magnetically interfering with each other. Thus, the scientist managed to pack bits only one nanometre apart.

"Looking at the shrinking of electronics components we wanted to know if this can be driven into the realm of single atoms," explains Loth. But instead of shrinking existing components the team chose the opposite approach: "Starting with the smallest thing -- single atoms -- we built data storage devices one atom at a time," says IBM research staff member Andreas Heinrich. The required precision is only mastered by few research groups worldwide.

"We tested how large we have to build our unit to reach the realm of classical physics," explains Loth, who moved from IBM to CFEL four months ago. Twelve atoms emerged as the minimum with the elements used. "Beneath this threshold quantum effects blur the stored information." If these quantum effects can somehow be employed for an even denser data storage is currently a topic of intense research.

With their experiments the team have not only built the smallest magnetic data storage unit ever, but have also created an ideal testbed for the transition from classical to quantum physics. "We have learned to control quantum effects through form and size of the iron atom rows," explains Loth, leader of the Max Planck research group 'dynamics of nanoelectric systems' at CFEL in Hamburg and the Max-Planck-Institute for Solid State Research at Stuttgart, Germany. "We can now use this ability to investigate how quantum mechanics kicks in. What seperates quantum magnets from classical magnets? How does a magnet behave at the frontier between both worlds? These are exciting questions that soon could be answered."

A new CFEL laboratory offering ideal conditions for this research will enable Loth to follow up these questions. "With Sebastian Loth, one of the world's leading scientists in the field of time-resolved scanning tunneling microscopy has joined CFEL," stresses CFEL research coordinator Ralf Köhn. "This perfectly complements our existing expertise for the investigation of the dynamics in atomic and molecular systems."