Monday, April 12, 2010

SCIENTISTS DISCOVER WORLDS SMALLEST SUPERCONDUCTOR

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Scientists have discovered the world’s smallest superconductor, a sheet of four pairs of molecules less than one nanometer wide. The Ohio University-led study, published as an advance online publication in the journal Nature Nanotechnology, provides the first evidence that nanoscale molecular superconducting wires can be fabricated, which could be used for nanoscale electronic devices and energy applications.

“Researchers have said that it’s almost impossible to make nanoscale interconnects using metallic conductors because the resistance increases as the size of wire becomes smaller. The nanowires become so hot that they can melt and destruct. That issue, Joule heating, has been a major barrier for making nanoscale devices a reality,” said lead author Saw-Wai Hla, an associate professor of physics and astronomy with Ohio University’s Nanoscale and Quantum Phenomena Institute.

Superconducting materials have an electrical resistance of zero, and so can carry large electrical currents without power dissipation or heat generation. Superconductivity was first discovered in 1911, and until recently, was considered a macroscopic phenomenon. The current finding suggests, however, that it exists at the molecular scale, which opens up a novel route for studying this phenomenon, Hla said. Superconductors currently are used in applications ranging from supercomputers to brain imaging devices.

In the new study, which was funded by the U.S. Department of Energy, Hla’s team examined synthesized molecules of a type of organic salt, (BETS)2-GaCl4, placed on a surface of silver. Using scanning tunneling spectroscopy, the scientists observed superconductivity in molecular chains of various lengths. For chains below 50 nanometers in length, superconductivity decreased as the chains became shorter. However, the researchers were still able to observe the phenomenon in chains as small as four pairs of molecules, or 3.5 nanometers in length.

To observe superconductivity at this scale, the scientists needed to cool the molecules to a temperature of 10 Kelvin. Warmer temperatures reduced the activity. In future studies, scientists can test different types of materials that might be able to form nanoscale superconducting wires at higher temperatures, Hla said.

“But we’ve opened up a new way to understand this phenomenon, which could lead to new materials that could be engineered to work at higher temperatures,” he said.

The study also is noteworthy for providing evidence that superconducting organic salts can grow on a substrate material.

“This is also vital if one wants to fabricate nanoscale electronic circuits using organic molecules,” Hla added.

(Photo: Saw-Wai Hla and Kendal Clark, Ohio University)

Ohio University

EARLY WARNING SYSTEM WOULD PREDICT SPACE STORMS ON MARS

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NASA’s vision for a permanent human presence on Mars as soon as 2028 will need to address the danger posed by space weather storms. These cyclical winds carrying storms comprised of high-energy particles occur every 11 years, with waves lingering for approximately three years before dying down.

Part of the colonists’ survival will depend on an early warning system that can predict these invisible, but deadly storms approaching Mars and signal an “all clear” when the danger passes, says Roger Dube, professor in the Chester F. Carlson Center for Imaging Science at Rochester Institute of Technology.

Dube has won NASA funding to develop a monitoring system that will provide this level of protection for people on Mars. As an additional benefit, the technology will give advanced warning of space storms threatening the critical infrastructure here on Earth, including the power grid, GPS navigation and sensitive communication satellites.

The system Dube envisions includes sensors and small solar observatories at the Mars colony or near the planetary pole for continual view of the solar surface. Special purpose satellites already positioned between the sun and the Earth will require advanced sensors and algorithms to detect signs of a dangerous flux of particles in order to provide warnings to both Earth and Mars.

“The technology we’re building uses existing satellites and solar telescopes that are in orbit or in space,” says Dube. “Our innovation will be to add artificial intelligence to the recognition of space storms. Initially the technology will be used to calculate the probability of the Earth being hit by a space weather storm, and once we’ve got that we’ll determine the orbital calculations for Mars.”

“Mars does not enjoy the defenses against such storms that Earth has,” Dube notes.

During a space storm, hurricane-force gusts hit Mars at full force. The winds, containing X-rays and particle rays emitted from solar flares and coronal mass ejections—clumps of high-energy particles belched by the sun—sweep past the planet’s weak magnetic field and atmosphere and strike the surface directly.

Even though the Earth’s strong magnetic field provides significant protection against these storms, severe storms can momentarily penetrate that defense. Magnetic portals in the Earth’s atmosphere have been observed that make our planet susceptible to the effects of severe space weather storms despite its strong magnetic field and atmospheric layers.

“When the wave of particles comes, it can be so intense that it actually bends the Earth’s magnetic field way beyond where it naturally belongs to a point where the magnetic field lines nearly cross. When they bend that much, everything snaps and you get this huge deposit of charge at the poles that can go all the way to the equator,” Dube says.

The charge is reflected in the ribbons of light known as the aurora borealis and carries the potential for creating havoc on Earth. The same high-energy particles can cripple the power grid by inducing currents into the network and can expose airplane passengers to radiation.

The Space Radiation Analysis Group at Johnson Space Center in Houston, in conjunction with the National Oceanic and Atmospheric Administration, regularly issues alerts to power suppliers and commercial airline carriers within 30 to 60 minutes of a storm. Dube thinks a better monitoring system could provide at least three days advanced warning for people living on Earth and Mars.

“We’ve got different types of data from different sources, such as images that show the coronal mass ejections,” Dube says. “We’ve got satellites orbiting between the sun and the earth monitoring the particle flux, and we have historical records that take us back in time that tell us what things looked like in the past. We’re looking to correlate all of these things together to see if there is a predictor that says, ‘Here comes a storm.’ ”

Dube’s team includes imaging science graduate student Santosh Suresh. His work visualizes data downloaded from three radio frequency receivers tuned to the ionosphere, the layer of Earth’s atmosphere made up of a molecule-rich plasma charged by solar radiation. The ionosphere observatory at RIT functions as a space weather station and consists of antennae attached to buildings on and around the RIT campus.

(Photo: RIT)

Rochester Institute of Technology

JEFFERSON SCIENTISTS UNLOCK SECRET TO POWERFUL TUMOR SUPPRESSOR THAT CAN REVERSE CANCER PROGRESSION

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Researchers at the Kimmel Cancer Center at Jefferson have discovered how a powerful tumor suppressor called DACH1 works – a finding that explains why restoring its lost function in cancer cells pushes them to become normal again.

In the March 29 online early edition of the Proceedings of the National Academy of Sciences (PNAS), the researchers say that DACH1 is a potent transcription factor whose protein binds to and forms a lock, of sorts, that stops more than 1,500 human genes from being activated. Some of these genes have been previously shown to promote cancer. When DACH1 isn’t around the expression levels of these genes increase because another well-known cancer promoting protein, forkhead, slots into the unlocked genes and turns them on.

“While the study was conducted mainly in breast cancer cells, the beneficial function of DACH1 is missing in a wide variety of cancers, and restoring it might offer us a new clinical strategy for these cancers,” says Chenguang Wang, Ph.D., a co-leader of the study and an assistant professor in the Department of Stem Cell Biology and Regenerative Medicine.

The study is remarkable not only because it describes the molecular function of DACH1 – a feat that took the research team 10 years to uncover – but the scientists scanned the human genome to see what genes DACH1 interact with, says study co-leader Richard Pestell, M.D., Ph.D., Director of the Kimmel Cancer Center and Chairman of the Department of Cancer Biology.

“The studies identify a new mechanism by which this important tumor suppressor works, and by interrogating the entire human genome these studies identified all the genes that bind and are regulated by DACH1,” Pestell says. “This is a major accomplishment.” DACH1 is the human version of the so-called Dachshund (Dac) gene first discovered in Drosophila, which are small fruit flies. Flies born without this gene have shorter than normal legs – hence the Dachshund reference – and don’t develop their eyes. Because Dac is, therefore, a key gene involved in development and growth, the Jefferson researchers started looking at its role in different cancers in the 1990s. “We knew that genes that direct growth in embryonic development can be switched on or off in cancer,” says Wang.

Wang, Pestell and their laboratories discovered that DACH1 function was missing in human breast cancer, as well as in prostate and endometrial cancers. They also showed that DACH1 represses tumor initiation and progression, and when DACH1 is put back into the cancer cell lines and in animals, cancer cells revert to a normal state. “When tumor cells begin to express this gene again, it not only reverses the cancer progression, but these cells begin to excrete molecules that stop surrounding tumor cells from growing as well,” Wang says. “It is really remarkable.”

But the researchers did not know how DACH1 was functioning, and this study explains the mechanism.

The scientists solved the puzzle by first identifying the binding sequence by which DACH1’s protein latches on to genes, and then they used several approaches (computer based and laboratory cell work) to identify the genes within the human genome that DACH1 interacts with. They identified 1,606 genes that have a promoter region that matches the DACH1 protein binding site. “These genes are potentially regulated by DACH1, which means that DACH1 is a transcription factor for these genes,” Wang says.

More work established that DACH1 is a transcriptional “repressor,” meaning that it binds to genes in order to keep them from being activated. Many tumor suppressors are also transcription factors, but they work by turning genes on. “For example, p53, the best known tumor suppressor, is an activator of genes,” he says. “This is the first time to identify DACH1 as a transcription factor to represses gene expression.”

The scientists also discovered that the DACH1 binding site resembles the binding site for a protein known as FOXM1known to be over-expressed in breast cancer. FOXM1 is a member of the FOX (Forkhead box) family of more than 100 transcription factors that regulate genes involved in cell growth and proliferation.

“In this manner a fundamental connection was made between DACH1 and the forkhead family of genes that regulate metabolism and stem cells,” Pestell says.

Because DACH1 is not available to put a lock on genes involved in cancer, Forkhead proteins latch on and activate those genes, the researchers say. “FOX is over-expressed in cancer and DACH1 is down-regulated,” Wang says. “If DACH1 is made available, FOX proteins cannot bind, and a cancer cell reverts back to its normal state.

“What is most intriguing is that DACH1 seems to be more powerful than a traditional tumor suppressor gene because when tumor cells suddenly express it, surrounding cancer cells also become normal again,” he says. “If we can find a way to turn this gene back on in breast cancers, and potentially other cancer types, we may be able to reverse the cancer progression.”

Jefferson University Hospitals

AFTER THE NEXT SUNSET, PLEASE TURN RIGHT

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Despite the fact that bats are active after sunset, they rely on the sun as their most trusted source of navigation. Researchers from the Max Planck Institute for Ornithology found that the greater mouse-eared bat orients itself with the help of the earth’s magnetic field at night and calibrates this compass to the sun's position at sunset (published online in Proceedings of the National Academy of Science, PNAS, March 29th, 2010).

Since the 1940s it has been known that bats use echolocation calls for orientation at close range. Some bats, however, fly 20 km and more away from their roost every night to search for prey. Summer and winter roosts are often over 50 km apart and some species migrate even up to 1000 km each year across Europe. Recent evidence has shown that bats utilise the Earth’s magnetic field for orientation on longer journeys. Scientists of the Max Planck Institute for Ornithology have now confirmed this finding after conducting research on the ability of greater mouse-eared bats to find their way home at night after manipulations of the magnetic field at sunset.

First, Richard Holland, Ivailo Borissov and Björn Siemers wanted to discover if bats are able to orient themselves at an unknown location. To do so, they captured bats and released them 25 km from their roost cave. They followed their flights with the help of small radio transmitters. Already at 1-3 km distance, most bats were heading home in the direction of their cave. "I was quite sceptical that this first part of the experiment would work," says Björn Siemers. "Therefore I was very impressed that the fastest bats arrived back in their cave only two hours after release". The precise question the researchers wanted to answer was: is this ability for orientation in unknown territory somehow related to perception of the magnetic field? And, further to this, do the bats then calibrate their magnetic compass to the sun like migrating birds?

The three researchers altered the direction of the magnetic field from north to east for half of the bats during sunset with the help of a device called a Helmholtz coil. And in contrast to the control group, these bats flew about 90 degrees east instead of south to their home cave. The decisive last part of the experiment was to repeat the procedure at night. Again the magnetic field of half of the bats was turned from north to east, but only after all signs of sunset had vanished from the sky. In this case the bats with an altered magnetic field flew in the same direction as the control bats. "The manipulation of the magnetic field was only effective in combination with the sunset", says Richard Holland. "Greater mouse-eared bats used the position of the sun at sunset as the most reliable indication of direction, and calibrated the magnetic field with it to use it as a compass later that night". For the bats, sunset means west, regardless to what their actual magnetic field is telling them. Due to iron deposits in the local earth’s crust, the magnetic field is known to vary unpredictably. It seems therefore that the animals find the sun to be a more trustworthy source for direction. This result is remarkable, given that this species usually emerges from their caves after sunset. "After the bats became active, we were able to see where the sun had disappeared even an hour after sunset", says Björn Siemers. This ‘glow’ seemed to be sufficient for the bats orientation.

(Photo: Dietmar Nill)

Max Planck Institute

EXTREME WEATHER IMPACTS MIGRATORY BIRDS

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Every year, hurricanes and droughts wreak havoc on human lives and property around the world. And according to a pair of new NASA-funded studies, migratory birds also experience severe impacts to their habitats and populations from these events.

While this may not seem like a revelation, the researchers were surprised to find that migratory bird species located as far as 60 miles (100 kilometers) from a hurricane’s path had experienced a long-term loss in population. Those populations took up to five years to rebound from the damage to their forest environments.

At the same time, researchers found that some migratory bird species could experience population losses as high as 13 percent when rainfall levels fall dramatically and cause drought in plains regions. The studies appear in the March edition of Global Change Biology.

"These studies suggest that whether a hurricane or a drought batters an area, migratory habits -- whether birds migrate south or stay put after breeding season -- are a strong predictor of how birds will fare," said Anna Pidgeon, an avian ecologist at the University of Wisconsin-Madison and a NASA-funded co-author of both studies.

"We believe changes in weather and climate are fundamental drivers of migration but, until now, we’ve known little of how changes in climate compel changes in migratory patterns," said Woody Turner, manager of the biodiversity program at NASA’s Headquarters in Washington. "The correlations don’t necessarily mean the environment alone is forcing migratory changes, but they offer a good place to start looking."

Pidgeon and other researchers see birds as excellent indicators of overall environmental health. Birds can give advance notice of ecosystem changes that will affect humans in time, while also telling us about the broader impacts of our actions.

Pidgeon, along with colleagues from NASA, the U.S. Department of Agriculture's Forest Service, the University of Maryland-College Park, and the University of Wisconsin-Madison, grouped 77 bird species into "migratory guilds." The guilds were based on similar migratory habits: birds that migrate long distances (to the tropics or subtropics), short distances, or reside solely in one location; breeding habitats: urban, semi-arid, or water-based habitats; the type of nests they construct; and whether they nest on or close to the ground or in tree canopies.

At the outset, researchers believed intuitively that hurricanes would cause losses among tree nesters due to a wipe-out of habitat from downed trees. That would bring gains for ground- and shrub nesters because of the increase in ground vegetation and nesting resources.

Pidgeon’s research team examined five Gulf and Atlantic Coast areas affected by hurricanes between 1984 and 2005. They used population and diversity data from the North American Breeding Bird Survey, tracks of hurricanes, and a time-series of digital images from the NASA-built Landsat remote sensing satellite. When matched to data on breeding seasons, the scientists found that destruction of habitat correlated with varying degrees of distress on the bird species. Habitat destruction caused losses in abundance and diversity across all species in the season following hurricanes, which persisted as long as five years.

Hurricanes pose no immediate danger to bird conservation, Pidgeon believes, provided there remains ample and suitable forest habitat to which birds can shift in the aftermath of a major storm.

In a separate study, Pidgeon and colleagues identified periods of drought and their subsequent impact on bird species. They started with a measure of the amount and quality of refuge for birds -- the Normalized Difference Vegetation Index (NDVI), which assesses the seasonal "greenness" of the landscape. The method involves using data from a satellite-based radiometer that measures the color of the landscape in different wavelengths according to a plant’s ability to absorb radiation. The stronger the reflectance of wavelengths off Earth’s surface, the greater density of green leaves on the ground.

When they compared this "greenness" against 15 years of precipitation data from 1,600 weather stations across the plains of North America, the team found that precipitation is a better means of forecasting bird survival during drought. "Rows of corn may be a sign of vegetation when viewed in a satellite image, but they don’t help protect birds during a drought because they’re not essential habitat," Pidgeon explained.

Whether researchers considered bird species together or in groups, according to whether they stay in an area all year versus spending the winter to the south, they always found that precipitation, rather than "greenness," was more strongly associated with species diversity and abundance.

"Satellite remote sensing is helping us see and analyze the ecological impact of these events on bird populations, as well as marine species and mammals," says climatologist Bill Patzert of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. "Ultimately, however, hurricanes, drought, and other influences act as part of natural selection."

(Photo: U.S. Fish and Wildlife Service)

NASA

COMMON MECHANISMS OF DRUG ABUSE AND OBESITY

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Some of the same brain mechanisms that fuel drug addiction in humans accompany the emergence of compulsive eating behaviors and the development of obesity in animals, according to research funded by the National Institute on Drug Abuse (NIDA), a component of the National Institutes of Health.

The study, conducted by researchers at the Scripps Research Institute, was released today in the online version of Nature Neuroscience and will also appear in the journal's May 2010 print issue. When investigators gave rats access to varying levels of high-fat foods, they found unrestricted availability alone can trigger addiction-like responses in the brain, leading to compulsive eating behaviors and the onset of obesity.

"Drug addiction and obesity are two of the most challenging health problems in the United States," said Dr. Nora D. Volkow, director of NIDA. "This research opens the door for us to apply some of the knowledge we have gathered about drug addiction to the study of overeating and obesity."

Both obesity and drug addiction have been linked to a dysfunction in the brain’s reward system. In both cases overconsumption can trigger a gradual increase in the reward threshold — requiring more and more palatable high fat food or reinforcing drug to satisfy the craving over time.

Researchers conducted this study in three groups of male rats over a 40-day period. Each day, the three groups had unlimited access to standard lab food. In addition, two of the groups also had access to high-fat, cafeteria style foods for short (one-hour) or long (18-23 hours) periods.

After 40 days, all groups were denied access to the high-fat foods. Throughout the study, researchers observed the feeding behaviors of each group, noting caloric intake, weight gain, and brain response.

The results support the notion that type 2 dopamine receptors (D2DR) — brain receptors that have been shown to play a key role in addiction — also play a key role in the rats' heightened response to food. In fact, as the rats became obese, the levels of D2DR in the brain's reward circuit decreased. This drop in D2DR is similar to that previously seen in humans addicted to drugs like cocaine or heroin.

"The results of this study could provide insight into a mechanism for obesity," said Paul J. Kenny, one of the study's co-authors and an associate professor at the Scripps Jupiter, Fla., research facility. "It's possible that drugs developed to treat addiction may also benefit people who are habitual overeaters."

Study results also suggest that environmental factors, such as increased or unlimited access to high-fat food options, can contribute to the problem of obesity.

"Hopefully, this study will change the way people think about eating," said Paul Johnson, a co-author and graduate student in the department of molecular therapeutics. "It demonstrates how just the availability of food can trigger overconsumption and obesity."

The National Institutes of Health

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