Bats, dolphins, and mole rats inspire advances in ultrasound technology
November 14, 2011
Sonar and ultrasound, which use sound as a navigational device and to paint accurate pictures of an environment, are the basis of countless technologies, including medical ultrasound machines and submarine navigation systems. But when it comes to more accurate sonar and ultrasound, animals’ “biosonar” capabilities still have the human race beat.
But not for long. In a new project that studies bats, dolphins, and mole rats, Prof. Nathan Intrator of Tel Aviv University’s Blavatnik School of Computer Science, in collaboration with Brown University’s Prof. Jim Simmons, is working to identify what gives biosonar the edge over human-made technologies. Using a unique method for measuring how the animals interpret the returning signals, Prof. Intrator has determined that the key to these animals’ success is superior, real-time data processing. “Animal ‘echolocations’ are done in fractions of milliseconds, at a resolution so high that a dolphin can see a tennis ball from approximately 260 feet away,” he says, noting that the animals are able to process several pieces of information simultaneously.
Their research, which has been reported in the Journal of the Acoustical Society of America and presented at the2010 and 2011 MLSP conferences,could lead to cutting-edge navigation systems and more accurate medical imaging.
Detecting “shape” from sound
Biosonar animals send ultrasonic sounds called “pings” into the environment. The shape of the returning signals, or echoes, determines how these animals “see” their surroundings, helping them to navigate or hunt for prey. In a matter of tens of milliseconds, the neurons in the animal’s brain are capable of a full-scale analysis of their surroundings represented in three dimensions, with little energy consumption. Even with the aid of a supercomputer, which consumes thousands of times more energy, humans cannot produce such an accurate picture, Prof. Intrator says. With echolocation, a bat can tell the difference between a fly in motion or at rest, or determine which of two fruits is heavier by observing their movements in the wind.
Intrigued by the quality of the natural world’s biosonar over its man-made equivalents, Profs. Intrator and Simmons set out to study how biosonar animals perform echo location so quickly and accurately. Using an electronic system, they altered the frequency and noise levels of the echo returned to the animal.
By manipulating the echo, the researchers could determine what factors of the returning signal reduced an animal’s ability to correctly analyze the returns. This in turn led to a better understanding of how the returning echoes are represented and analyzed in the animal’s brain.
A more accurate view of the human body
Prof. Intrator and his fellow researchers have created mathematical models, involving machine learning and signal processing, that improve man’s ability to interpret the echoes.This will lead to more accurate echo localization and better resilience to background noise.
Once researchers gather more information about animal interpretation of biosonar, they will be able to mimic this technology for better ultrasound and sonar systems, says Prof. Intrator. “Animals explore pings with multiple filters or receptive fields, and we have demonstrated that exploring each ping in multiple ways can lead to higher accuracy,” he explains. “By understanding sonar animals, we can create a new family of ultrasound systems that will be able to explore our bodies with more accurate medical imaging.”
This could provide a variety of benefits to the medical field, such as earlier detection of defects in embryos or non-invasive detection of cancer tumors. Unlike an MRI or CT machine, which are large, expensive to operate, and often use dangerous radiation, the new generation of ultrasound machines could be used in a doctor’s office at a fraction of the cost. The research could also benefit military reconnaissance efforts both underwater and underground.
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Contact: George Hunka
ghunka@aftau.org
212-742-9070
American Friends of Tel Aviv University
Diseased hearts to heal themselves in future
November 11, 2011
Cellular reversion processes arise in diseases of the heart muscle, for example myocardial infarction and cardiomyopathy, which limit the fatal consequences for the organ. Scientists from the Max Planck Institute for Heart and Lung Research in Bad Nauheim and the Schüchtermann Klinik in Bad Rothenfelde have identified a protein which fulfils a central task in this reversion process by stimulating the regression of individual heart muscle cells into their precursor cells. It is now planned to improve the self-healing powers of the heart with the help of this protein.
In order to regenerate damaged heart muscle as caused by a heart attack, for example, the damaged muscle cells must be replaced by new ones. The number of cells to be replaced may be considerable, depending on the extent of the damage caused. Simpler vertebrates like the salamander adopt a strategy whereby surviving healthy heart muscle cells regress into an embryonic state. This process, which is known as dedifferentiation, produces cells which contain a series of stem cell markers and re-attain their cell division activity. Thus, new cells are produced which convert, in turn, into heart muscle cells. The cardiac function is then restored through the remodelling of the muscle tissue.
An optimised repair mechanism of this kind does not exist in humans. Although heart stem cells were discovered some time ago, exactly how and to what extent they play a role in cardiac repair is a matter of dispute. It has only been known for a few years that processes comparable to those found in the salamander even exist in mammals.
Thomas Braun’s research group at the Max Planck Institute for Heart and Lung Research in Bad Nauheim has now discovered the molecule responsible for controlling this dedifferentiation of heart muscle cells in mammals. The scientists initially noticed the high concentration of oncostatin M in tissue samples from the hearts of patients suffering from myocardial infarction. It was already known that this protein is responsible for the dedifferentiation of different cell types, among other things. The researchers therefore treated cultivated heart muscle cells with oncostatin M in the laboratory and were then able to trace the regression of the cells live under the microscope: “Based on certain changes in the cells, we were able to see that almost all heart muscle cells had been dedifferentiated within six days of treatment with oncostatin M,” explains Braun. “We were also able to demonstrate the presence of various stem cell markers in the cells. This should be understood as an indicator that these cells had been switched to a repair mode.”
Using a mouse infarct model, the Max Planck researchers succeeded in demonstrating that oncostatin M actually does stimulate the repair of damaged heart muscle tissue as presumed. One of the two test groups had been modified genetically in advance to ensure that the oncostatin M could not have any effect in these animals. “The difference between the two groups was astonishing. Whereas in the group in which oncostatin M could take effect almost all animals were still alive after four weeks, 40 percent of the genetically modified mice had died from the effects of the infarction,” says Braun. The reason for this was that oncostatin M ensured clearly quantifiable better cardiac function in the unmodified animals.
The scientists in Bad Nauheim would now like to find a way of using oncostatin M in treatment. The aim is to strengthen the self-healing powers of the damaged heart muscle and to enable the restoration of cardiac function for the first time. The downside, however, is that oncostatin M was also observed to be counterproductive and exacerbated the damage in an experiment on a chronically diseased heart. “We believe that oncostatin M has considerable potential for efficiently healing damaged heart muscle tissue. What we now need is to be able to pinpoint the precise window of application to prevent any possible negative effects,” says Braun.
Original publication:
Thomas Kubin, Jochen Pöling, Sawa Kostin, Praveen Gajawada, Stefan Hein, Wolfgang Rees, Astrid Wietelmann, Minoru Tanaka, Holger Lörchner, Silvia Schimanski, Marten Szibor, Henning Warnecke, Thomas Braun: Oncostatin M Is a Major Mediator of Cardiomyocyte Dedifferentiation and Remodeling. Cell Stem Cell 9, 420, 2011
Contact: Professor Thomas Braun
thomas.braun@mpi-bn.mpg.de
49-603-270-51102
Max-Planck-Gesellschaft
Giant planet ejected from the solar system
November 10, 2011
Just as an expert chess player sacrifices a piece to protect the queen, the solar system may have given up a giant planet and spared the Earth, according to an article recently published in The Astrophysical Journal Letters.
“We have all sorts of clues about the early evolution of the solar system,” says author Dr. David Nesvorny of the Southwest Research Institute. “They come from the analysis of the trans-Neptunian population of small bodies known as the Kuiper Belt, and from the lunar cratering record.”
These clues suggest that the orbits of giant planets were affected by a dynamical instability when the solar system was only about 600 million years old. As a result, the giant planets and smaller bodies scattered away from each other.
Some small bodies moved into the Kuiper Belt and others traveled inward, producing impacts on the terrestrial planets and the Moon. The giant planets moved as well. Jupiter, for example, scattered most small bodies outward and moved inward.
This scenario presents a problem, however. Slow changes in Jupiter’s orbit, such as the ones expected from interaction with small bodies, would have conveyed too much momentum to the orbits of the terrestrial planets. Stirring up or disrupting the inner solar system and possibly causing the Earth to collide with Mars or Venus.
“Colleagues suggested a clever way around this problem,” says Nesvorny. “They proposed that Jupiter’s orbit quickly changed when Jupiter scattered off of Uranus or Neptune during the dynamical instability in the outer solar system.” The “jumping-Jupiter” theory, as it is known, is less harmful to the inner solar system, because the orbital coupling between the terrestrial planets and Jupiter is weak if Jupiter jumps.
Nesvorny conducted thousands of computer simulations of the early solar system to test the jumping-Jupiter theory. He found that, as hoped for, Jupiter did in fact jump by scattering from Uranus or Neptune. When it jumped, however, Uranus or Neptune was knocked out of the solar system. “Something was clearly wrong,” he says.
Motivated by these results, Nesvorny wondered whether the early solar system could have had five giant planets instead of four. By running the simulations with an additional giant planet with mass similar to that of Uranus or Neptune, things suddenly fell in place. One planet was ejected from the solar system by Jupiter, leaving four giant planets behind, and Jupiter jumped, leaving the terrestrial planets undisturbed.
“The possibility that the solar system had more than four giant planets initially, and ejected some, appears to be conceivable in view of the recent discovery of a large number of free-floating planets in interstellar space, indicating the planet ejection process could be a common occurrence,” says Nesvorny.
This research was funded by the National Lunar Science Institute and the National Science Foundation. The paper, “Young Solar System’s Fifth Giant Planet?” by Dr. David Nesvorny was published online by The Astrophysical Journal Letters.
Contact: Maria I. Martinez
mmartinez@swri.org
210-522-3305
Southwest Research Institute
Potential new NASA mission would reveal the hearts of undead stars
November 9, 2011
Neutron stars have been called the zombies of the cosmos, shining on even though they’re technically dead, and occasionally feeding on a neighboring star if it gets too close.
They are born when a massive star runs out of fuel and collapses under its own gravity, crushing the matter in its core and blasting away its outer layers in a supernova explosion that can outshine a billion suns.
The core, compressed by gravity to inconceivable density – one teaspoon would weigh about a billion tons on Earth – lives on as a neutron star. Although the nuclear fusion fires that sustained its parent star are extinguished, it still shines with heat left over from its explosive formation, and from radiation generated by its magnetic field, which became intensely concentrated as the core collapsed, and can be over a trillion times stronger than Earth’s.
Although its parent star could easily have been more than a million miles across, a neutron star is only about the size of a city. However, its intense gravity makes it the ultimate trash compactor, capable of packing in an astonishing amount of matter, more than 1.4 times the content of the Sun, or at least 460,000 Earths.
“A neutron star is right at the threshold of matter as it can exist – if it gets any denser, it becomes a black hole,” says Dr. Zaven Arzoumanian of NASA’s Goddard Space Flight Center in Greenbelt, Md.
Arzoumanian is Deputy Principal Investigator on a proposed mission called the Neutron Star Interior Composition Explorer (NICER) that would unveil the dark heart of a neutron star. “We have no way of creating neutron star interiors on Earth, so what happens to matter under such incredible pressure is a mystery – there are many theories about how it behaves. The closest we come to simulating these conditions is in particle accelerators that smash atoms together at almost the speed of light. However, these collisions are not an exact substitute – they only last a split second, and they generate temperatures that are much higher than what’s inside neutron stars.”
If NASA approves it for construction, the mission will be launched by the summer of 2016 and attached robotically to the International Space Station. In September 2011, NASA selected NICER for study as a potential Explorer Mission of Opportunity. The mission will receive $250,000 to conduct an 11-month implementation concept study. Five Mission of Opportunity proposals were selected from 20 submissions. Following the detailed studies, NASA plans to select for development one or more of the five Mission of Opportunity proposals in February 2013.
NICER’s array of 56 telescopes will collect X-rays generated both from hotspots on a neutron star’s surface and from its powerful magnetic field. There are two hotspots on a neutron star at opposite sides, one at each magnetic pole, the place where the star’s intense magnetic field emerges from the surface. Here, particles trapped in the magnetic field rain down and generate X-rays when they strike the surface. X-rays are an energetic form of light invisible to human eyes but detectable by special instruments. As the hotspots rotate into our line of sight, they produce a pulse of light, like a lighthouse beam, giving rise to the stars’ alternate name, pulsars.
Many pulsars flash several times per second, because of the rapid rotation they inherit as they are born. All stars rotate, and as the parent star’s core shrinks, it spins faster, like a twirling ice skater pulling in her arms. A neutron star’s powerful gravity can also pull in gas from a neighboring star if it orbits too closely. This infalling gas can spin up a neutron star to even higher speeds; some rotate hundreds of times per second.
The key to understanding how matter behaves inside a neutron star is pinning down the correct Equation Of State (EOS) that most accurately describes how matter responds to increasing pressure. Currently, there are many suggested EOSs, each proposing that matter can be compressed by different amounts inside neutron stars. Suppose you held two balls of the same size, but one was made of foam and the other was made of wood. You could squeeze the foam ball down to a smaller size than the wooden one. In the same way, an EOS that says matter is highly compressible will predict a smaller neutron star for a given mass than an EOS that says matter is less compressible.
So if researchers know a neutron star’s mass, all they need to do is find out how big it is to get the correct EOS and unlock the secret of what matter does under extreme gravity. “The problem is that neutron stars are small, and much too far away to allow their sizes to be measured directly,” says NICER Principal Investigator Dr. Keith Gendreau of NASA Goddard. “However, NICER will be the first mission that has enough sensitivity and time-resolution to figure out a neutron star’s size indirectly. The key is to precisely measure how much the brightness of the X-rays changes as the neutron star rotates.”
This change in brightness with time is called a star’s light curve, and it appears as a wavy line on a graph.
Because neutron stars pack so much mass into such a tiny volume, they generate strong gravity that actually bends space (and distorts time) in accordance with Einstein’s theory of General Relativity. This warping of space enables researchers to determine a neutron star’s mass if it has a nearby companion, either another neutron star or a white dwarf, a lower-density object that is the core remnant of a less-massive star. Neutron stars with these companions are actually fairly common.
The warping of space produces effects like an orbital shift called precession, which makes the orbit move like a hula-hoop around a dancer. Also, as the neutron star and its companion move around each other, they create ripples in space called gravitational waves. These waves carry away orbital energy, so the neutron star and its companion gradually move closer together and their orbit shrinks. NICER will measure these effects over time, and the greater these effects, the more mass the neutron star has.
Warped space also will let the NICER team figure out a neutron star’s size. Suppose we have a neutron star lined up so that you can only see one hotspot, the one on the near side that faces us. As it rotates into view, the brightness increases until the hotspot is pointed directly at us, then the brightness decreases as it rotates away.
This alignment makes the star’s brightness highly variable – it’s quite bright when the hotspot is pointed at us, and very dim when the hotspot is on the far side out of our view. The drastic change in brightness produces a light curve with large waves, with deep troughs when the star is dim.
However, since light must follow the contours of space, warped space bends light. The distorted space around the neutron star bends its light so much that you can see parts of the far side, including the other hotspot. With the second hotspot visible, at least part of the time, you have bright light more often, so the brightness doesn’t change as much. This makes a light curve that appears smoother, with smaller waves.
If a woman wearing stiletto heels walks on a trampoline, she will warp the surface more than if she wears snowshoes. In the same way, the more compact a neutron star is, the more it will bend space and light. This will allow us to see the far-side hotspot more often, which will make its X-ray brightness less variable, and the star will produce a smoother light curve.
The team has models that produce unique light curves for the various sizes predicted by different EOSs. By choosing the light curve that best matches the observed one, they will get the correct EOS and solve the riddle of matter on the edge of oblivion.
Contact: Bill Steigerwald
william.a.steigerwald@nasa.gov
301-286-5017
NASA/Goddard Space Flight Center
Ancient DNA provides new insights into cave paintings of horses
November 7, 2011
An international team of researchers has used ancient DNA to shed new light on the realism of horses depicted in prehistoric cave paintings.
The team, which includes researchers from the University of York, has found that all the colour variations seen in Paleolithic cave paintings – including distinctive ‘leopard’ spotting – existed in pre-domestic horse populations, lending weight to the argument that the artists were reflecting their natural environment.
The study, published in Proceedings of the National Academy of Sciences (PNAS) today, is also the first to produce evidence for white spotted phenotypes in pre-domestic horses. Previous ancient DNA studies have only produced evidence for bay and black horses.
Archaeologists have long debated whether works of art from the Paleolithic period, particularly cave paintings, are reflections of the natural environment or have deeper abstract or symbolic meanings.
This is particularly true of the cave painting “The Dappled Horses of Pech-Merle” in France, which dates back more than 25,000 years and clearly depicts white horses with dark spots.
The dappled horses’ spotted coat pattern bears a strong resemblance to a pattern known as ‘leopard’ in modern horses. However, as some researchers believed a spotted coat phenotype unlikely at this time, pre-historians have often argued for more complex explanations, suggesting the spotted pattern was in some way symbolic or abstract.
Researchers from the UK, Germany, USA, Spain, Russia and Mexico genotyped and analysed nine coat-colour loci in 31 pre-domestic horses dating back as far as 35,000 years ago from Siberia, Eastern and Western Europe and the Iberian Peninsula. This involved analysing bones and teeth specimens from 15 locations.
They found that four Pleistocene and two Copper Age samples from Western and Eastern Europe shared a gene associated with leopard spotting, providing the first evidence that spotted horses existed at this time.
In addition, 18 horses had a bay coat colour and seven were black, meaning that all colour phenotypes distinguishable in cave paintings – bay, black and spotted – existed in pre-domestic horse populations.
Professor Michi Hofreiter, from the Department of Biology at the University of York, said: “Our results suggest that, at least for wild horses, Paleolithic cave paintings, including the remarkable depictions of spotted horses, were closely rooted in the real-life appearance of animals.
“While previous DNA studies have produced evidence for bay and black horses, our study has demonstrated that the leopard complex spotting phenotype was also already present in ancient horses and was accurately depicted by their human contemporaries nearly 25,000 years ago.
“Our findings lend support to hypotheses that argue that cave paintings constitute reflections of the natural environment of humans at the time and may contain less of a symbolic or transcendental connotation than often assumed.”
The data and laboratory work were led by Dr Melanie Pruvost, from the Department of Evolutionary Genetics at the Leibniz Institute for Zoo and Wildlife Research and the Department of Natural Sciences at the German Archaeological Institute, both in Berlin. The results were replicated in laboratories at the University of York.
Dr Pruvost said: “We are just starting to have the genetic tools to access the appearance of past animals and there are still a lot of question marks and phenotypes for which the genetic process has not yet been described. However, we can already see that this kind of study will greatly improve our knowledge about the past. Knowing that leopard spotting horses were present during the Pleistocene in Europe provides new arguments or insights for archaeologists to interpret cave arts.”
Dr Arne Ludwig, from the Leibniz Institute for Zoo and Wildlife Research in Berlin, added: “Although taken as a whole, images of horses are often quite rudimentary in their execution, some detailed representations, from both Western Europe and the Ural mountains, are realistic enough to at least potentially represent the actual appearance of the animals when alive.
“In these cases, attributes of coat colours may also have been depicted with deliberate naturalism, emphasizing colours or patterns that characterised contemporary horses.”
Exact numbers of Upper Paleolithic sites with animal depictions are uncertain because of ongoing debates about the taxonomic identification of some images and dating. However, art of this period has been identified in at least 40 sites in the Dordogne-Périgord region, a similar number in coastal Cantabria and around a dozen sites in both the Ardèche and Ariège regions.
Where animal species can be confidently identified, horses are depicted at the majority of these sites.
Professor Terry O’Connor from the University of York’s Department of Archaeology was involved in the interpretation of the results. He said: “Representations of animals from the Paleolithic period have the potential to provide first-hand insights into the physical environment that humans encountered thousands of years ago. However, the motivation behind, and therefore the degree of realism in these depictions is hotly debated.
“The depictions of horses at Pech-Merle in particular have generated a great deal of debate. The spotted horses are featured in a frieze which includes hand outlines and abstract patterns of spots. The juxtaposition of elements has raised the question of whether the spotted pattern is in some way symbolic or abstract, especially since many researchers considered a spotted coat phenotype unlikely for Paleolithic horses.
“However, our research removes the need for any symbolic explanation of the horses. People drew what they saw, and that gives us greater confidence in understanding Paleolithic depictions of other species as naturalistic illustrations.”
Leopard complex spotting in modern horses is characterised by white spotting patterns that range from horses having a few white spots on the rump to horses that are almost completely white. The white area of these horses can also have pigmented oval spots known as ‘leopard spots’.
Dr. Monika Reissmann, from Humboldt University’s Department for Crop and Animal Sciences, explained: “This phenotype was in great demand during the Baroque Age. But in the following centuries the leopard complex phenotype went out of fashion and became very rare. Today leopard complex is a popular phenotype in several horse breeds including Knabstrupper, Appaloosa and Noriker and breeding efforts have intensified again because there is a growing interest in the restoration of these horses.”
The fact that four out of 10 of the Western European horses from the Pleistocene had a genotype indicative of the leopard complex phenotype, suggests that this phenotype was not rare in Western Europe during this period.
However, bay seems to have been the most common colour phenotype in pre-domestic times with 18 out of the 31 samples having bay genotypes. This is also the most commonly painted phenotype in the Paeolithic period.
Contact: Caron Lett
caron.lett@york.ac.uk
44-190-432-2029
University of York
A 2-dimensional electron liquid solidifies in a magnetic field
November 4, 2011
Physicists from the Georgia Institute of Technology have developed a theory that describes, in a unified manner, the coexistence of liquid and pinned solid phases of electrons in two dimensions under the influence of a magnetic field. The theory also describes the transition between these phases as the field is varied. The theoretical predictions by Constantine Yannouleas and Uzi Landman, from Georgia Tech’s School of Physics, aim to explain and provide insights into the origins of experimental findings published last year by a team of researchers from Princeton, Florida State and Purdue universities. The research appears in the October 27 edition of the journal Physical Review B.
The experimental discovery in 1982 of a new Hall conductance step at a fraction ν=1/m with m=3, that is at (1/3)e2/h (with more conductance steps, at other m, found later) – where h is the Planck constant and e is the electron charge – was made for two-dimensional electrons at low temperatures and strong magnetic fields and was greeted with great surprise. The theoretical explanation of this finding a year later by Robert Laughlin in terms of a new form of a quantum fluid, earned him and the experimentalists Horst Störmer and Daniel Tsui the 1998 Nobel Prize with the citation “for the discovery of a new form of quantum fluid with fractionally charged excitations.” These discoveries represent conceptual breakthroughs in the understanding of matter, and the fractional quantum Hall effect (FQHE) liquid states, originating from the highly correlated nature of the electrons in these systems, have been termed as new states of matter.
“The quantum fluid state at the 1/3 primary fraction is the hallmark of the FQHE, whose theoretical understanding has been formulated around the antithesis between a new form of quantum fluid and the pinned Wigner crystal,” said Landman, Regents’ and Institute Professor in the School of Physics, F.E. Callaway Chair and director of the Center for Computational Materials Science (CCMS) at Georgia Tech. “Therefore, the discovery of pinned crystalline signatures in the neighborhood of the 1/3 FQHE fraction, measured as resonances in the microwave spectrum of the two-dimensional electron gas and reported in the Physical Review Letters in September 2010 by a group of researchers headed by Daniel Tsui, was rather surprising,” he added.
Indeed, formation of a hexagonally ordered two-dimensional electron solid phase, a so called Wigner crystal (WC) named after the Nobel laureate physicist Eugene Wigner who predicted its existence in 1934, has been anticipated for smaller quantum Hall fractional fillings, ν, of the lowest Landau level populated by the electrons at high magnetic fields, for example ν = 1/9, 1/7 and even 1/5. However, the electrons in the ν=1/3 fraction were believed to resist crystallization and remain liquid.
The Georgia Tech physicists developed a theoretical formalism that, in conjunction with exact numerical solutions, provides a unified microscopic approach to the interplay between FQHE liquid and Wigner solid states in the neighborhood of the 1/3 fractional filling. A major advantage of their approach is the use of a single class of variational wave functions for description of both the quantum liquid and solid phases.
“Liquid characteristics of the fractional quantum Hall effect states are associated with symmetry-conserving vibrations and rotations of the strongly interacting electrons and they coexist with intrinsic correlations that are crystalline in nature,” Yannouleas and Landman wrote in the opening section of their paper. “While the electron densities of the fractional quantum Hall effect liquid state do not exhibit crystalline patterns, the intrinsic crystalline correlations which they possess are reflected in the emergence of a sequence of liquid states of enhanced stability, called cusp states, that correspond in the thermodynamic limit to the fractional quantum Hall effect filling fractions observed in Hall conductance measurements,” they added.
The key to their explanation of the recent experimental observations pertaining to the appearance of solid characteristics for magnetic fields in the neighborhood of the 1/3 filling fraction is their finding that “away from the exact fractional fillings, for example near ν=1/3, weak pinning perturbations, due to weak disorder, may overcome the energy gaps between adjacent good angular momentum symmetry-conserving states. The coupling between these states generates broken-symmetry ground states whose densities exhibit spatial crystalline patterns. At the same time, however, the energy gap between the ground state at ν=1/3 and adjacent states is found to be sufficiently large to prevent disorder-induced mixing, thus preserving its quantum fluid nature.”
Furthermore, the work shows that the emergence of the crystalline features, via the pinning perturbations, is a consequence of the aforementioned presence of crystalline correlations in the symmetry-conserving states. Consequently, mixing rules that govern the nature of the disorder-pinned crystalline states have been formulated and tested. Extrapolation of the calculated results to the thermodynamic limit shows development of a hexagonal Wigner crystal with enhanced stability due to quantum correlations.
“In closing, the nature of electrons in the fractional quantum Hall regime continues now for close to three decades to be a subject of great fascination, a research field that raises questions whose investigations can lead to deeper conceptual understanding of matter and many-body phenomena, and a rich source of surprise and discovery,” said Landman.
This work was supported by the Office of Basic Energy Sciences of the US Department of Energy.
Contact: Jason Maderer
maderer@gatech.edu
404-385-2966
Georgia Institute of Technology
Watching the birth of an iceberg
November 2, 2011
After discovering an emerging crack that cuts across the floating ice shelf of Pine Island Glacier in Antarctica, NASA’s Operation IceBridge has flown a follow-up mission and made the first-ever detailed airborne measurements of a major iceberg calving in progress.
NASA’s Operation Ice Bridge, the largest airborne survey of Earth’s polar ice ever flown, is in the midst of its third field campaign from Punta Arenas, Chile. The six-year mission will yield an unprecedented three-dimensional view of Arctic and Antarctic ice sheets, ice shelves and sea ice.
Pine Island Glacier last calved a significant iceberg in 2001, and some scientists have speculated recently that it was primed to calve again. But until an Oct. 14 IceBridge flight of NASA’s DC-8, no one had seen any evidence of the ice shelf beginning to break apart. Since then, a more detailed look back at satellite imagery seems to show the first signs of the crack in early October.
While Pine Island has scientists’ attention because it is both big and unstable – scientists call it the largest source of uncertainty in global sea level rise projections – the calving underway now is part of a natural process for a glacier that terminates in open water. Gravity pulls the ice in the glacier westward along Antarctica’s Hudson Mountains toward the Amundsen Sea. A floating tongue of ice reaches out 30 miles into the Amundsen beyond the grounding line, the below-sea-level point where the ice shelf locks onto the continental bedrock. As ice pushes toward the sea from the interior, inevitably the ice shelf will crack and send a large iceberg free.
“We are actually now witnessing how it happens and it’s very exciting for us,” said IceBridge project scientist Michael Studinger, Goddard Space Flight Center, Greenbelt, Md. “It’s part of a natural process but it’s pretty exciting to be here and actually observe it while it happens. To my knowledge, no one has flown a lidar instrument over an actively developing rift such as this.”
A primary goal of Operation IceBridge is to put the same instruments over the exact same flight lines and satellite tracks, year after year, to gather meaningful and accurate data of how ice sheets and glaciers are changing over time. But discovering a developing rift in one of the most significant science targets in the world of glaciology offered a brief change in agenda for the Oct. 26 flight, if only for a 30-minute diversion from the day’s prescribed flight lines.
The IceBridge team observed the rift running across the ice shelf for about 18 miles. The lidar instrument on the DC-8, the Airborne Topographic Mapper, measured the rift’s shoulders about 820 feet apart (250 meters) at its widest, although the rift stretched about 260 feet wide along most of the crack. The deepest points from the ice shelf surface ranged 165 to 195 feet (50 to 60 meters). When the iceberg breaks free it will cover about 340 square miles (880 square kilometers) of surface area. Radar measurements suggested the ice shelf in the region of the rift is about 1,640 feet (500 meters) feet thick, with only about 160 feet of that floating above water and the rest submerged. It is likely that once the iceberg floats away, the leading edge of the ice shelf will have receded farther than at any time since its location was first recorded in the 1940s.
Veteran DC-8 pilot Bill Brockett first flew the day’s designed mission, crisscrossing the flow of the glacier near the grounding line to gather data on its elevation, topography and thickness. When it came time to investigate the crack, Brockett flew across it before turning to fly along the rift by sight. The ATM makes its precision topography maps with a laser than scans 360 degrees 20 times per second, while firing 3,000 laser pulses per second. When flying at an altitude of 3,000 feet, as during this flight, it measures a swath of the surface about 1,500 feet wide. As the crack measured at more than 800 feet wide in places, it was important for Brockett to hold tight over the crevasse.
“The pilots did a really nice job of keeping the aircraft and our ATM scan swath pretty much centered over the rift as you flew from one end to the other,” said Jim Yungel, who leads the ATM team out of NASA’s Wallops Island Flight Facility in Virginia. “It was a real challenge to be told we’re going to attempt to fly along it and let’s see if your lidar systems can map that crack and can map the bottom of the crack.
“And it was a lot of fun on a personal level to see if something that you built over the years can actually do a job like that. So, yeah, I enjoyed it. I really enjoyed seeing the results being produced.”
While the ATM provided the most detailed measurements of the topography of the rift, other instruments onboard the DC-8 also captured unique aspects. The Digital Mapping System, a nadir-view camera, gathered high-definition close-ups of the craggy split. On the flight perpendicular to the crack, the McCORDS radar also measured its depth and the thickness of the ice shelf in that region.
Catching the rift in action required a bit of luck, but is also testimony to the science benefit of consistent, repeated trips and the flexibility of a manned mission in the field.
“A lot of times when you’re in science, you don’t get a chance to catch the big stories as they happen because you’re not there at the right place at the right time,” said John Sonntag, Instrument Team Lead for Operation IceBridge, based at Goddard Space Flight Center. “But this time we were.”
Contact: Adam Voiland
adam.p.voiland@nasa.gov
301-352-4631
NASA/Goddard Space Flight Center
Babies understand thought process of others at 10 months old, MU research finds
November 1, 2011
New research from the University of Missouri indicates that at 10 months, babies start to understand another person’s thought process, providing new insights on how humans acquire knowledge and how communication develops.
“Understanding other people is a key factor in successful communication, and humans start to understand this at a very young age,” said Yuyan Luo, associate professor of developmental psychology in the MU College of Arts and Science. “Our study indicates that infants, even before they can verbally communicate, can understand the thought processes of other people – even if the thoughts diverge from what the infants know as truth, a term psychologists call false belief.”
During the study, infants were monitored during different trials of a common psychological test in which an actor indicated preference for certain objects. Researchers timed the infant’s gaze, which is an indication of infant knowledge. The infants watched longer when the actor’s preferences changed. This led the researchers to believe that infants understood how the actor interacted with the objects.
“When the actor did not witness the removal or addition of the preferred object, the infants seemed to use that information to interpret the person’s actions,” Luo said. “The infants appear to recognize that the actor’s behavior comes from what the actor could see or could not see and hence what the actor thinks, and this finding is consistent with similar false belief studies that involve older children.”
Luo said her study is one of the first to explore the false belief understanding in the first year of life; evidence from other studies indicates that infant understanding could be present at an earlier age. As the research moves forward, Luo expects to find more understanding of how humans learn to communicate.
“In adults, beliefs guide behavior, but it would be difficult to explain another person’s behavior without explaining his or her mental state,” Luo said.
The study, “Do 10-month-old infants understand others’ false beliefs?” is published in the journal Cognition.
Contact: Steven Adams
AdamsST@missouri.edu
573-882-8353
University of Missouri-Columbia
Planets smashed into dust near supermassive black holes
October 29, 2011
Fat doughnut-shaped dust shrouds that obscure about half of supermassive black holes could be the result of high speed crashes between planets and asteroids, according to a new theory from an international team of astronomers. The scientists, led by Dr. Sergei Nayakshin of the University of Leicester, publish their results in the journal Monthly Notices of the Royal Astronomical Society.
Supermassive black holes reside in the central parts of most galaxies. Observations indicate that about 50% of them are hidden from view by mysterious clouds of dust, the origin of which is not completely understood. The new theory is inspired by our own Solar System, where the so-called zodiacal dust is known to originate from collisions between solid bodies such as asteroids and comets. The scientists propose that the central regions of galaxies contain not only black holes and stars but also planets and asteroids.
Collisions between these rocky objects would occur at colossal speeds as large as 1000 km per second, continuously shattering and fragmenting the objects, until eventually they end up as microscopic dust. Dr. Nayakshin points out that this harsh environment – radiation and frequent collisions – would make the planets orbiting supermassive black holes sterile, even before they are destroyed. “Too bad for life on these planets”, he says, “but on the other hand the dust created in this way blocks much of the harmful radiation from reaching the rest of the host galaxy. This in turn may make it easier for life to prosper elsewhere in the rest of the central region of the galaxy.”
He also believes that understanding the origin of the dust near black holes is important in our models of how these monsters grow and how exactly they affect their host galaxies. “We suspect that the supermassive black hole in our own Galaxy, the Milky Way, expelled most of the gas that would otherwise turn into more stars and planets”, he continues, “Understanding the origin of the dust in the inner regions of galaxies would take us one step closer to solving the mystery of the supermassive black holes”.
CONTACTS
Dr Sergei Nayakshin
Department of Physics and Astronomy
University of Leicester
Leicester LE1 7RH
United Kingdom
Tel: 44-116-252-2454
Email: sn85@leicester.ac.uk
Peter Thorley
Press Office
University of Leicester
Tel: 44-116-252-2415
Email: pt91@leicester.ac.uk
IMAGE AND CAPTION
A related image is available from
http://www.spacetelescope.org/news/heic0617/
Caption: “”Light echo” of dust illuminated by a nearby star V838 Monocerotis as it became 600,000 times more luminous than our Sun in January 2002. The flash is believed to have been caused by a giant collision of some kind, e.g., between two stars or a star and a planet. Credit: NASA/ESA. Collsions of smaller objects, such as asteroids or minor planets near a supermassive black hole could also be dramatic due to the huge collision velocities and would release a lot of dust.”
FURTHER INFORMATION
The new work is published in “Are SMBHs shrouded by “Super-Oort” clouds of comets and asteroids?”, Nayakshin S., Sazonov S., Sunayev R., Monthly Notices of the Royal Astronomical Society, in press. A preprint can be seen at http://arxiv.org/abs/1109.1217
Contact: Dr Sergei Nayakshin
sn85@leicester.ac.uk
44-011-625-22454
University of Leicester
Physicists manipulate single molecules to unravel secrets of protein folding
October 27, 2011
Physicists at the Technische Universitaet Muenchen (TUM) are opening a new window into the life of biological cells, using a technique that lets them grab the ends of a single protein molecule and pull, making continuous, direct measurements as it unfolds and refolds. Their latest results, reported in the journal Science, reveal a complex network of intermediate structural and kinetic states along the way to functionally correct folded forms, including both express routes and dead ends. Better understanding of protein folding is essential because incorrectly folded proteins cause diseases such as Alzheimer’s and Parkinson’s. The experiments focused on the protein calmodulin, which is not implicated in these diseases but plays a role in many processes vital to cellular functions, and thus to human health.
The functions (and malfunctions) of proteins are largely determined by their structures, so researchers are exploring many avenues toward understanding precisely how they fold (or misfold). Where X-ray structural analyses offer “snapshots” of protein folding, single-molecule force spectroscopy — the approach pioneered by Prof. Matthias Rief and colleagues in the TUM Department of Physics — produces views that are, by comparison, more like movies. Even though these movies are very “blurred,” since they only capture the length of the molecule, they allow the researchers to study the dynamics of the folding process.
In the study reported in Science, Rief’s co-authors were TUM doctoral candidates Johannes Stigler, Fabian Ziegler, Anja Gieseke, and Christof Gebhardt (now a postdoc at Harvard University). A grant from the TUM Institute for Advanced Study helped the laboratory acquire the instrumentation that made these single-molecule experiments possible — ultra-stable, high-resolution “optical tweezers,” a tool that traps miniscule objects between opposing laser beams as surely as if they were being held between thumb and forefinger.
To get a grip on a calmodulin molecule, the researchers first would insert it between two molecules of a mechanically tougher protein called ubiquitin. Residues of the amino acid cysteine at the outer ends of this assembly allowed “handles” made of DNA to be attached, and these were fixed to glass beads one micrometer in diameter. The beads, and thus the calmodulin molecule between them, could then be manipulated with the optical tweezers. The essence of the experiments, repeated many times over in a variety of ways, was to pull the ends of a single, folded calmodulin molecule until it straightened out and then to reduce the tension so it could fold again, constantly measuring protein length, mechanical forces and time with extreme precision. Throughout, the calmodulin molecule was kept in conditions not too different from its working environment inside a cell, an aqueous solution with a concentration of calcium ions known to favor stable folding. Statistical analysis helped to reveal what the measurements recorded.
The results indicate that distinct subdomains of the calmodulin molecule fold independently yet interact with others, sometimes cooperating and sometimes interfering. “Far from being a simple two-state process,” Rief explains, “the folding of a calmodulin molecule takes place via a complex network of pathways in what we call its ‘energy landscape.’ We found that this map of kinetic states and paths between different folded forms includes dead ends — intermediate structures that need to be undone, like unwanted knots in a rope, before the protein can assume a shape that enables it to function properly.” The researchers also discovered express routes, pathways that let some domains reach their final state much more rapidly than the molecule as a whole.
“The calmodulin molecule,” Rief says, “even though considered small compared to most proteins in our body, already exhibits unexpected complexity in its folding. Nature manages to fold much more complex proteins without major misfoldings. Understanding this still remains a challenge for the future, and single-molecule experiments will help to resolve it.”
Original publication:
The Complex Folding Network of Single Calmodulin Molecules
Johannes Stigler, Fabian Ziegler, J. Christof M. Gebhardt, Matthias Rief
Science, Oct. 28, 2011, pp. 512-516
DOI: 10.1126/science.1207598
Contact:
Prof. Matthias Rief
Department of Physics E22
Technische Universitaet Muenchen
James-Franck-Strasse
85748 Garching, Germany
Tel: +49 89 289 12471
E-mail: mrief@ph.tum.de
Home page: http://bio.ph.tum.de/home/e22-prof-dr-rief/rief-home.html
Technische Universitaet Muenchen (TUM) is one of Europe’s leading universities. It has roughly 460 professors, 9000 academic and non-academic staff, and 31,000 students. It focuses on the engineering sciences, natural sciences, life sciences, medicine, and economic sciences. After winning numerous awards, it was selected as an “Elite University” in 2006 by the Science Council (Wissenschaftsrat) and the German Research Foundation (DFG). The university’s global network includes an outpost with a research campus in Singapore. TUM is dedicated to the ideal of a top-level research-based entrepreneurial university. http://www.tum.de
Contact: Patrick Regan
regan@zv.tum.de
49-892-891-0515
Technische Universitaet Muenchen