星空体育频道: 2013-08-25

2013年8月31日星期六

Sea-level rise drives shoreline retreat in Hawaii

The authors of the work point out that knowing that SLR is a primary cause of shoreline change on a regional scale allows managers and other coastal zone decision-makers to target SLR impacts in their research programs and long-term planning. This study is confirmation that future SLR is a major concern for decision-makers charged with managing beaches.

"It is common knowledge among coastal scientists that sea level rise leads to shoreline recession," stated Dr. Brad Romine, coastal geologist with the University of Hawaii Sea Grant College Program. "Shorelines find an equilibrium position that is a balance between sediment availability and rising ocean levels. On an individual beach with adequate sediment availability, beach processes may not reflect the impact of SLR. With this research we confirm the importance of SLR as a primary driver of shoreline change on a regional to island-wide basis."

Globally-averaged sea-level rose at about 2 mm per year over the past century. Previous studies indicate that the rate of rise is now approximately 3 mm per year and may accelerate over coming decades. The results of the recent publication show that SLR is an important factor in historical shoreline change in Hawaii and will be increasingly important with projected SLR acceleration in this century. "Improved understanding of the influence of SLR on historical shoreline trends will aid in forecasting beach changes with increasing SLR," said Dr. Charles Fletcher, Associate Dean and Professor of Geology and Geophysics at the UHM SOEST.

"The research being conducted by SOEST provides us with an opportunity to anticipate SLR effects on coastal areas, including Hawaii's world famous beaches, coastal communities, and infrastructure. We hope this information will inform long range planning decisions and allow for the development of SLR adaptation plans," said Sam Lemmo, Administrator, Department of Land and natural Resources, Office of Conservation and Coastal Lands.

Results of island-wide historical trends indicate that Maui beaches are significantly more erosional than beaches on Oahu. On Maui, 78% of beaches eroded over the past century with an overall (island-wide) average shoreline change rate of 13 cm of erosion per year, while 52% of Oahu beaches eroded with an overall average shoreline change rate of 3 cm of erosion per year.

The variation in long-term relative SLR rates along the Hawaii archipelago is due, in large part, to variations in island subsidence with distance from actively growing Hawaii Island and/or variations in upper ocean water masses. The islands of Oahu and Maui, Hawaii, with significantly different rates of localized sea-level rise (SLR has been approximately 65% higher rate on Maui) over the past century, provided a natural laboratory to investigate possible relations between historical shoreline changes and SLR.

Island-wide and regional historical shoreline trends were calculated for the islands using shoreline positions measured from aerial photographs and survey charts. Shoreline positions were manually digitized using photogrammetric and geographic information system (GIS) software from aerial photo mosaics and topographic and hydrographic survey charts provided by the National Ocean Service (NOS). Shoreline movement through time was measured using GIS software. Historical shoreline data were optimized to reduce anthropogenic influences (e.g., constructing seawalls or sand mining) on shoreline change measurements. The researchers controlled for influences other than SLR to determine if SLR remains as the best explanation for observed changes. They also utilized a series of consistency checks to determine if results are significant and to eliminate other possible explanations.

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Sideline teleconcussion robot to be tested at football games

Mayo Clinic will be working with NAU to test the feasibility of using a telemedicine robot to assess athletes with suspected concussions during football games as part of a research study. With sophisticated robotic technology, use of a specialized remote controlled camera system allows patients to be "seen" by the neurology specialist, miles away, in real time. During the study, the robot equipped with a specialized camera system, remotely operated by a Mayo Clinic neurologist located in Phoenix who has the ability to assess a player for symptoms and signs of a concussion and to consult with sideline medical personnel.

The first time the robot will be used in a game is this Friday, Aug. 30 when NAU kicks off its season against the University of Arizona in Tucson at 7 p.m. (MST).

"Athletes at professional and collegiate levels have lobbied for access to neurologic expertise on the sideline. As we seek new and innovative ways to provide the highest level of concussion care and expertise, we hope that teleconcussion can meet this need and give athletes at all levels immediate access to concussion experts," said Bert Vargas, M.D., a neurologist at Mayo Clinic who is heading up the research.

This study would be the first to explore whether a remote neurological assessment is as accurate as a face-to-face evaluation in identifying concussion symptoms and making return to play decisions. Mayo Clinic physicians will not provide medical consultations during the study, they will only assess the feasibility of using the technology. If it appears feasible, this may open the door for countless schools, athletic teams, and organizations without access to specialized care to use similar portable technology for sideline assessments.

"As nearly 60 percent of U.S. high schools do not have access to an athletic trainer, youth athletes, who are more susceptible to concussion and its after-effects, have the fewest safeguards in place to identify possible concussion signs and symptoms at the time of injury, Dr. Vargas says. "Teleconcussion is one way to bridge this gap regardless of when or where they may be playing."

Others involved collegiate sports agree.

"At NAU, our primary goal is to provide an outstanding student-athlete experience culminating in graduation," says Dr. Lisa Campos, vice president for Intercollegiate Athletics at Northern Arizona University. "We charge our staff to research the most current and best practices to ensure the safety and care of our students. Partnering with the Mayo Clinic in its telemedicine study will further this research and potentially improve diagnosis for rural areas that may not have access to team doctors or neurologists. The study allows the NAU Sports Medicine Staff and team doctors to continue to make all diagnoses and return to play decisions for our students, while investigating the effectiveness and efficiencies of telemedicine. We are excited to have the teleconcussion robot on our sideline this fall."

"There were a number of examples last football season where college football players clearly demonstrating concussion-like symptoms were quickly thrown back in games or weren't even taken out of the game for an evaluation," said Ramogi Huma, executive director of the National College Players Association. "College football players are in desperate need for independent concussion experts on the sidelines, and this study could help make that safeguard a reality."

Mayo Clinic in Arizona first used telemedicine technology with the telestroke program in 2007, when statistics revealed that 40 percent of residents in Arizona did not live in an area where they were availed of stroke expertise. Mayo Clinic was the first medical center in Arizona to do pioneering clinical research to study telemedicine as a means of serving patients with stroke in non-urban settings, and today serves as the "hub" in a network of 12 "spoke" centers, all but one in Arizona. Since the telestroke program began nearly 3,000 emergency consultations for neurological emergencies like stroke between Mayo neurologists and physicians at the spoke centers have taken place.

In 2011, Mayo Clinic expanded its telemedicine evaluations to include concussion evaluations. Concussion experts at the Mayo Clinic Comprehensive Concussion Program in Arizona coined the term "teleconcussion" and described the concept as an effective means to assess concussed patients in a case study published in the December 2012 issue of Telemedicine and e-Health.

"Teleconcussion is an excellent new example of connected care in action, as athletes with suspected concussion, anywhere and anytime, can be effectively connected to Mayo Clinic concussion knowledge and expertise," says Bart Demaerschalk, M.D., co-author of study, Director of Mayo Clinic Teleneurology and Telestroke, and Chair of American Academy of Neurology Telemedicine Work Group.

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Researchers a step closer to finding cosmic ray origins

Cosmic rays can damage electronics on Earth, as well as human DNA, putting astronauts in space especially at risk.

The research, which draws on data collected by IceTop, the IceCube Observatory's surface array of detectors, is published online in Physical Review D, a leading journal in elementary particle physics.

University of Delaware physicist Bakhtiyar Ruzybayev is the study's corresponding author. UD scientists were the lead group for the construction of IceTop with support from the National Science Foundation and coordination by the project office at the University of Wisconsin, Madison.

The more scientists learn about the energy spectrum and chemical composition of cosmic rays, the closer humanity will come to uncovering where these energetic particles originate.

Cosmic rays are known to reach energies above 100 billion giga-electron volts (1011 GeV). The data reported in this latest paper cover the energy range from 1.6 times 106 GeV to 109 GeV.

Researchers are particularly interested in identifying cosmic rays in this interval because the transition from cosmic rays produced in the Milky Way Galaxy to "extragalactic" cosmic rays, produced outside our galaxy, is expected to occur in this energy range.

Exploding stars called supernovae are among the sources of cosmic rays here in the Milky Way, while distant objects such as collapsing massive stars and active galactic nuclei far from the Milky Way are believed to produce the highest energy particles in nature.

As Ruzybayev points out, the cosmic-ray energy spectrum does not follow a simple power law between the "knee" around 4 PeV (peta-electron volts) and the "ankle" around 4 EeV (exa-electron volts), as previously thought, but exhibits features like hardening around 20 PeV and steepening around 130 PeV.

"The spectrum steepens at the 'knee,' which is generally interpreted as the beginning of the end of the galactic population. Below the knee, cosmic rays are galactic in origin, while above that energy, particles from more distant regions in our universe become more and more likely," Ruzybayev explained. "These measurements provide new constraints that must be satisfied by any models that try to explain the acceleration and propagation of cosmic rays."

IceTop consists of 81 stations in its final configuration, covering an area of one square kilometer on the South Pole surface above the detectors of IceCube, which are buried over a mile deep in the ice. The analysis presented in this article was performed using data taken from June 2010 to May 2011, when the array consisted of only 73 stations.

The IceCube collaboration includes nearly 250 people from 39 research institutions in 11 countries, including the University of Delaware.

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LED Lighting Proved: Why LED efficiency drops at high current

2013/08/30

04sep13Rensselaer Researchers at the US Rensselaer Polytechnic have proven a link between LED efficiency drop at high current and carrier mobility. Better lighting LEDs could result.

“Efficiency droop, first reported in 1999, has been a key obstacle in the development of LED lighting for situations, like household lighting, that call for economical sources of versatile and bright light,” said the university.

Published in Applied Physics Letters, the work shows that at high current an electric field develops within the p-type region of the diode allowing electrons to escape the active region where they would otherwise re-combine with holes to emit photons – a mechanism previously proposed, but not proven, said Rensselaer.

“We measure excellent correlation between the onset of field build-up and the onset of droop. This is clear evidence that the mechanism is electron leakage, and we can describe it quantitatively,” said Rensselaer researcher David Meyaard. “For example, in one result reported in the paper, we show the onset of high injection and the onset of droop and you can see that they are very nicely correlated. And that was just not possible in the past because there was really no theoretical model that described how electron leakage really works.”

“If the holes and the electrons had similar properties, there is a symmetry; both would meet in the middle, where the quantum well is, and there they recombine,” said Professor Fred Schubert. “What we have instead is a material system where the electrons are much more mobile than the holes. And because they are very mobile, they diffuse more easily, they also react more easily to an electric field. Because of that asymmetry, or disparity, we have a propensity of the electrons to shoot over and to be extracted from the quantum well. And so they don’t meet the hole in the active region and so they don’t emit light.”

Based on the theoretical model, Meyaard and Schubert will look for LED structures that reduce the issue.

The paper is ‘Identifying the cause of the efficiency droop in GaInN light-emitting diodes by correlating the onset of high injection with the onset of the efficiency droop.’

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2013年8月30日星期五

Hydrogen fuel from sunlight: Researchers make unique semiconductor/catalyst construct

"We've developed a method by which molecular hydrogen-producing catalysts can be interfaced with a semiconductor that absorbs visible light," says Gary Moore, a chemist with Berkeley Lab's Physical Biosciences Division and principal investigator for JCAP. "Our experimental results indicate that the catalyst and the light-absorber are interfaced structurally as well as functionally."

Moore is the corresponding author, along with Junko Yano and Ian Sharp, who also hold joint appointments with Berkeley Lab and JCAP, of a paper describing this research in the Journal of the American Chemical Society (JACS). The article is titled "Photofunctional Construct That Interfaces Molecular Cobalt-Based Catalysts for H₂ Production to a Visible-Light-Absorbing Semiconductor." Co-authors are Alexandra Krawicz, Jinhui Yang and Eitan Anzenberg.

Earth receives more energy in one hour's worth of sunlight than all of humanity uses in an entire year. Through the process of photosynthesis, green plants harness solar energy to split molecules of water into oxygen, hydrogen ions (protons) and free electrons. The oxygen is released as waste and the protons and electrons are used to convert carbon dioxide into the carbohydrate sugars that plants use for energy. Scientists aim to mimic the concept but improve upon the actual process.

JCAP, which has a northern branch in Berkeley and a southern branch on the campus of the California Institute of Technology (Caltech), was established in 2010 by DOE as an Energy Innovation Hub. Operated as a partnership between Caltech and Berkeley Lab, JCAP is the largest research program in the United States dedicated to developing an artificial solar-fuel technology. While artificial photosynthesis can be used to generate electricity, fuels can be a more effective means of storing and transporting energy. The goal is an artificial photosynthesis system that's at least 10 times more efficient than natural photosynthesis.

To this end, once photoanodes have used solar energy to split water molecules, JCAP scientists need high performance semiconductor photocathodes that can use solar energy to catalyze fuel production. In previous efforts to produce hydrogen fuel, catalysts have been immobilized on non-photoactive substrates. This approach requires the application of an external electrical potential to generate hydrogen. Moore and his colleagues have combined these steps into a single material.

"In coupling the absorption of visible light with the production of hydrogen in one material, we can generate a fuel simply by illuminating our photocathode," Moore says. "No external electrochemical forward biasing is required."

The new JCAP photocathode construct consists of the semiconductor gallium phosphide and a molecular cobalt-containing hydrogen production catalyst from the cobaloxime class of compounds. As an absorber of visible light, gallium phosphide can make use of a greater number of available solar photons than semiconductors that absorb ultraviolet light, which means it is capable of producing significantly higher photocurrents and rates of fuel production. However, gallium phosphide can be notoriously unstable during photoelectrochemical operations.

Moore and his colleagues found that coating the surface of gallium phosphide with a film of the polymer vinylpyridine alleviates the instability problem, and if the vinylpyridine is then chemically treated with the cobaloxime catalyst, hydrogen production is significantly boosted.

"The modular aspect of our method allows independent modification of the light-absorber, linking material and catalyst, which means it can be adapted for use with other catalysts tethered over structured photocathodes as new materials and discoveries emerge," Moore says. "This could allow us, for example, to replace the precious metal catalysts currently used in many solar-fuel generator prototypes with catalysts made from earth-abundant elements."

Despite its promising electronic properties, gallium phosphide features a mid-sized optical band gap which ultimately limits the total fraction of solar photons available for absorption. Moore and his colleagues are now investigating semiconductors that cover a broader range of the solar spectrum, and catalysts that operate faster at lower electrical potentials. They also plan to investigate molecular catalysts for carbon dioxide reduction.

"We look forward to adapting our method to incorporate materials with improved properties for converting sunlight to fuel," Moore says. "We believe our method provides researchers at JCAP and elsewhere with an important tool for developing integrated photocathode materials that can be used in future solar-fuel generators as well as other technologies capable of reducing net carbon dioxide emissions."

This research was funded by the DOE Office of Science.

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Business Server CPU from Imagination next year

2013/08/30

Imagination intends to bring out a CPU for servers next year. The chip will be based on the MIPS architecture and will be aimed at low power hyperscale servers which are increasingly being required by big server farm operators like Google, Facebook and Microsoft.

Imagination bought MIPS for $100 million last year. “We didn’t acquire MIPS for the hell of it,” says Sir Hossein Yassaie, Imagination’s CEO, “the intent with MIPS is to cover all the markets where a CPU is relevant.”

Yassaie is preparing for a long-term play in servers. It was a seven year gestation for ARM from planning a server strategy to getting some revenues from server chips. “For us to be a significant player it will take several years,” says Yassaie.

For one thing, he’s got to find manufacturers willing to build Imagination CPUs into server ICs in a market dominated by x86.

But, post MIPS, Yassaie Is setting his sights high. “We are aiming to have 25 per cent market share of the CPU IP market,” says Yassaie.

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Learning how to migrate: Young whoopers stay the course when they follow a wise old bird

Aug. 29, 2013 — Scientists have studied bird migration for centuries, but it remains one of nature's great mysteries. How do birds find their way over long distances between breeding and wintering sites? Is their migration route encoded in their genes, or is it learned?

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Working with records from a long-term effort to reintroduce critically endangered whooping cranes in the Eastern U.S., a University of Maryland-led research team found evidence that these long-lived birds learn their migration route from older cranes, and get better at it with age.

Whooping crane groups that included a seven-year-old adult deviated 38% less from a migratory straight-line path between their Wisconsin breeding grounds and Florida wintering grounds, the researchers found. One-year-old birds that did not follow older birds veered, on average, 60 miles (97 kilometers) from a straight flight path. When the one-year-old cranes traveled with older birds, the average deviation was less than 40 miles (64 kilometers).

Individual whoopers' ability to stick to the route increased steadily each year up to about age 5, and remained roughly constant from that point on, the researchers found.

Many migration studies are done in short-lived species like songbirds, or by comparing a young bird to an older bird, said UMD biologist Thomas Mueller, an expert on animal migration and the study's lead scientist. "Here we could look over the course of the individual animals' lifetimes, and show that learning takes place over many years."

The researchers' findings, to be published August 30 in the journal Science, are based on data from an intensive effort to restore the endangered bird to its native range. The whooping crane (Grus americana), is North America's largest bird, standing five feet tall, and one of its longest-lived, surviving 30 years or more in the wild. The species was near extinction in the 1940s, with fewer than 25 individuals. Today about 250 wild whoopers summer in Canada and migrate to Texas for the winter.

The Whooping Crane Eastern Partnership, made up of government and non-profit experts, has been working since 2001 to establish a second population in the Eastern U.S., which now numbers more than 100 birds. At Maryland's Patuxent Wildlife Research Refuge and other captive breeding sites, adult whooping cranes produce chicks and biologists hand-raise them, using special methods designed to prepare the chicks for life in the wild. Each summer in a Wisconsin marsh, experts train a group of captive-raised chicks to follow an ultralight aircraft, using techniques like those portrayed in the fictional 1996 movie "Fly Away Home" to lead them on a 1,300-mile journey to their Florida wintering grounds.

Only this first migration is human-assisted; from then on the young birds travel on their own, usually in the company of other whooping cranes. Their movements are monitored daily via satellite transmitters, radio telemetry and on-the-ground observers. The result is a record of the movements of individual birds over several years, all with known parentage and the same upbringing.

"This is a globally unique data set in which we can control for genetics and test for the effect of experience," said UMD Biology Professor William F. Fagan, a co-author of the paper, "and it gives us an indication of just how important this kind of socially learned behavior is."

Using data on all the ultralight-trained birds' spring and fall migrations from 2002 to 2009, the researchers found that neither genetic relatedness nor gender had any effect on the whooping cranes' tendency to stay on the shortest migratory route. They were surprised to find that the migrating groups' size also made no difference.

"Many biologists would have expected to find a strong effect of group size," Fagan said, "with input from more birds' brains leading to improved navigation, but we didn't see that effect."

Only one experienced bird per group was enough to keep the migration on track. The researchers hypothesize that older birds are better at recognizing landmarks and coping with bad weather. Stronger autumn winds may explain why the whoopers tended to stray further from their straight course during fall migration, Mueller said.

The study shows the migration training for captive-born whooping cranes is working, Mueller said. However, the reintroduced whoopers are having trouble breeding in the wild. Based on the migration study's finding, "we need to take into consideration that these birds may also reproduce more successfully as they age," he said.

Given the whooping cranes' recent plunge towards extinction, it wouldn't be surprising if the birds need to re-learn how best to raise their chicks, said Patuxent-based scientist Sarah J. Converse of the U.S. Geological Survey, a co-author of the paper.

"These birds' behaviors have evolved over millennia," Converse said. "Managers here are trying to restore a culture, that is, the knowledge that these birds accumulate over time. We need to give these birds the time and the opportunity to get the breeding right. We might need to be a little bit patient."

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From cancer treatment to ion thruster: The newest little idea for nanosat micro rockets

Nanosatellites borrow many of their components from terrestrial gadgets: miniaturized cameras, wireless radios and GPS receivers that have been perfected for hand-held devices are also perfect for spacecraft. However, according to Michigan Technological University's L. Brad King, there is at least one technology need that is unique to space: "Even the best smartphones don't have miniaturized rocket engines, so we need to develop them from scratch."

Miniature rockets aren't needed to launch a nanosatellite from Earth. The small vehicles can hitchhike with a regular rocket that is going that way anyway. But because they are hitchhikers, these nanosats don't always get dropped off in their preferred location. Once in space, a nanosatellite might need some type of propulsion to move it from its drop-off point into its desired orbit. This is where the micro rocket engine comes in.

For the last few years, researchers around the world have been trying to build such rockets using microscopic hollow needles to electrically spray thin jets of fluid, which push the spacecraft in the opposite direction. The fluid propellant is a special chemical known as an ionic liquid. A single thruster needle is finer than a human hair, less than one millimeter long and produces a thrust force equivalent to the weight of a few grains of sand. A few hundred of these needles fit in a postage-stamp-size package and produce enough thrust to maneuver a nanosatellite.

These new electrospray thrusters face some design challenges, however. "Because they are so small and intricate, they are expensive to make, and the needles are fragile," says King, the Ron and Elaine Starr Professor of Mechanical Engineering-Engineering Mechanics. "They are easily destroyed either by a careless bump or an electrical arc when they're running."

To get around the problem, King and his team have developed an elegant strategy: eliminate the expensive and tedious microfabrication required to make the needles by letting Mother Nature take care of the assembly. "We're working with a unique type of liquid called a ferrofluid that naturally forms a stationary pattern of sharp tips in the liquid surface," he says. "Each tip in this self-assembling structure can spray a jet of fluid just like a micro-needle, so we don't actually have to make any needles."

Ferrofluids have been around since the 1960s. They are made of tiny magnetic particles suspended in a solvent that moves when magnetic force is applied. King illustrates with a tiny container holding a ferrofluid made of kerosene and iron dust. The fluid lies flat until he puts a magnet beneath it. Then suddenly, the liquid forms a regular series of peaks reminiscent of a mountain range or Bart Simpson's haircut. These peaks remain perfectly stable despite vigorous shaking and even turning the container upside down. It is, nonetheless, completely liquid, as a finger-tip touch proves undeniably. When the magnet is removed, the liquid relaxes to a perfectly flat surface.

King's team was trying to make an ionic liquid that behaved like a ferrofluid when they learned about a research team at the University of Sydney that was already making these substances. The Sydney team was using magnetic nanoparticles made by the life-sciences company Sirtex, which are used to treat liver cancer. "They sent us a sample, and we've used it to develop a thruster," King said. "Now we have a nice collaboration going. It's amazing that the same technology used to treat cancer can also function as a micro rocket for spacecraft."

King's first thruster is made of a one-inch block of aluminum containing a small ring of the special fluid. When a magnet is placed beneath the block, the liquid forms a tiny, five-tipped crown. When an electric force is then applied to the ferrofluid crown liquid jets emerge from each point, producing thrust. "It's fascinating to watch," King says. "The peaks get taller and skinnier, and taller and skinnier, and at some point the rounded tips instantly pop into nano-sharp points and start emitting ions."

The thruster appears to be almost immune to permanent damage. The tips automatically heal themselves and re-grow if they are somehow damaged. King's team has already demonstrated its self-healing properties, albeit inadvertently. "We accidentally turned the voltage up too high, and the tips exploded in a small arc," King says. While this would spell death for a typical thruster, "A completely new crown immediately formed from the remaining ferrofluid and once again resumed thrusting."

Their thruster isn't ready to push a satellite around in orbit just yet. "First we have to really understand what is happening on a microscopic level, and then develop a larger prototype based on what we learn," King said. "We're not quite there yet; we can't build a person out of liquid, like the notorious villain from the Terminator movies. But we're pretty sure we can build a rocket engine."

King has applied for a patent on the new technology. The research is funded by the Air Force Office of Scientific Research.

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Transparent artificial muscle plays music to prove a point

Aug. 29, 2013 — In a materials science laboratory at Harvard University, a transparent disk connected to a laptop fills the room with music -- it's the "Morning" prelude from Peer Gynt, played on an ionic speaker.

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No ordinary speaker, it consists of a thin sheet of rubber sandwiched between two layers of a saltwater gel, and it's as clear as a window. A high-voltage signal that runs across the surfaces and through the layers forces the rubber to rapidly contract and vibrate, producing sounds that span the entire audible spectrum, 20 hertz to 20 kilohertz.

But this is not an electronic device, nor has it ever been seen before. Published in the August 30 issue of Science, it represents the first demonstration that electrical charges carried by ions, rather than electrons, can be put to meaningful use in fast-moving, high-voltage devices.

"Ionic conductors could replace certain electronic systems; they even offer several advantages," says co-lead author Jeong-Yun Sun, a postdoctoral fellow at the Harvard School of Engineering and Applied Sciences (SEAS).

For example, ionic conductors can be stretched to many times their normal area without an increase in resistivity -- a problem common in stretchable electronic devices. Secondly, they can be transparent, making them well suited for optical applications. Thirdly, the gels used as electrolytes are biocompatible, so it would be relatively easy to incorporate ionic devices -- such as artificial muscles or skin -- into biological systems.

After all, signals carried by charged ions are the electricity of the human body, allowing neurons to share knowledge and spurring the heart to beat. Bioengineers would dearly love to mesh artificial organs and limbs with that system.

"The big vision is soft machines," says co-lead author Christoph Keplinger, who worked on the project as a postdoctoral fellow at Harvard SEAS and in the Department of Chemistry and Chemical Biology. "Engineered ionic systems can achieve a lot of functions that our body has: they can sense, they can conduct a signal, and they can actuate movement. We're really approaching the type of soft machine that biology has to offer."

The audio speaker represents a robust proof of concept for ionic conductors because producing sounds across the entire audible spectrum requires both high voltage (to squeeze hard on the rubber layer) and high-speed actuation (to vibrate quickly) -- two criteria which are important for applications but which would have ruled out the use of ionic conductors in the past.

The traditional constraints are well known: high voltages can set off electrochemical reactions in ionic materials, producing gases and burning up the materials. Ions are also much larger and heavier than electrons, so physically moving them through a circuit is typically slow. The system invented at Harvard overcomes both of these problems, opening up a vast number of potential applications including not just biomedical devices, but also fast-moving robotics and adaptive optics.

"It must seem counterintuitive to many people, that ionic conductors could be used in a system that requires very fast actuation, like our speaker," says Sun. "Yet by exploiting the rubber layer as an insulator, we're able to control the voltage at the interfaces where the gel connects to the electrodes, so we don't have to worry about unwanted chemical reactions. The input signal is an alternating current (AC), and we use the rubber sheet as a capacitor, which blocks the flow of charge carriers through the circuit. As a result, we don't have to continuously move the ions in one direction, which would be slow; we simply redistribute them, which we can do thousands of times per second."

Sun works in a research group led by Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at Harvard SEAS. An expert in the mechanical behaviors of materials, Suo is also a Kavli Scholar at the Kavli Institute for Bionano Science & Technology, which is based at SEAS.

Suo teamed up with George M. Whitesides, a prominent chemist who specializes in soft machines, among many other topics. Whitesides is the Woodford L. and Ann A. Flowers University Professor in the Department of Chemistry and Chemical Biology, co-director of the Kavli Institute at Harvard, and a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering at Harvard.

"We'd like to change people's attitudes about where ionics can be used," says Keplinger, who now works in Whitesides' research group. "Our system doesn't need a lot of power, and you can integrate it anywhere you would need a soft, transparent layer that deforms in response to electrical stimuli -- for example, on the screen of a TV, laptop, or smartphone to generate sound or provide localized haptic feedback -- and people are even thinking about smart windows. You could potentially place this speaker on a window and achieve active noise cancellation, with complete silence inside."

Sam Liss, Director of Business Development in Harvard's Office of Technology Development, is working closely with the Suo and Whitesides labs to commercialize the technology. Their plan is to work with companies in a range of product categories, including tablet computing, smartphones, wearable electronics, consumer audio devices, and adaptive optics.

"With wearable computing devices becoming a reality, you could imagine eventually having a pair of glasses that toggles between wide-angle, telephoto, or reading modes based on voice commands or gestures," suggests Liss.

For now, there is much more engineering and chemistry work to be done. The Harvard team chose to make its audio speaker out of very simple materials -- the electrolyte is a polyacrylamide gel swollen with salt water -- but they emphasize that an entire class of ionically conductive materials is available for experimentation. Future work will focus on identifying the best combinations of materials for compatibility, long life, and adhesion between the layers.

In addition to Keplinger, Sun, Whitesides, and Suo, coauthors included Keith Choon Chiang Foo, a former postdoctoral fellow at Harvard SEAS, now at the Institute of High Performance Computing in Singapore; and Philipp Rothemund, a graduate student at Harvard SEAS.

This research was supported by the National Science Foundation through a grant to the Materials Research Science and Engineering Center at Harvard University (DMR-0820484) and by the Army Research Office (W911NF-09-1-0476). It was also enabled in part by the Department of Energy (ER45852) and the Agency for Science, Technology, and Research (A*STAR), Singapore.

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NASA data reveals mega-canyon under Greenland ice sheet

Aug. 29, 2013 — Data from a NASA airborne science mission reveals evidence of a large and previously unknown canyon hidden under a mile of Greenland ice.

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The canyon has the characteristics of a winding river channel and is at least 460 miles (750 kilometers) long, making it longer than the Grand Canyon. In some places, it is as deep as 2,600 feet (800 meters), on scale with segments of the Grand Canyon. This immense feature is thought to predate the ice sheet that has covered Greenland for the last few million years.

"One might assume that the landscape of the Earth has been fully explored and mapped," said Jonathan Bamber, professor of physical geography at the University of Bristol in the United Kingdom, and lead author of the study. "Our research shows there's still a lot left to discover."

Bamber's team published its findings Thursday in the journal Science.

The scientists used thousands of miles of airborne radar data, collected by NASA and researchers from the United Kingdom and Germany over several decades, to piece together the landscape lying beneath the Greenland ice sheet.

A large portion of this data was collected from 2009 through 2012 by NASA's Operation IceBridge, an airborne science campaign that studies polar ice. One of IceBridge's scientific instruments, the Multichannel Coherent Radar Depth Sounder, can see through vast layers of ice to measure its thickness and the shape of bedrock below.

In their analysis of the radar data, the team discovered a continuous bedrock canyon that extends from almost the center of the island and ends beneath the Petermann Glacier fjord in northern Greenland.

At certain frequencies, radio waves can travel through the ice and bounce off the bedrock underneath. The amount of times the radio waves took to bounce back helped researchers determine the depth of the canyon. The longer it took, the deeper the bedrock feature.

"Two things helped lead to this discovery," said Michael Studinger, IceBridge project scientist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It was the enormous amount of data collected by IceBridge and the work of combining it with other datasets into a Greenland-wide compilation of all existing data that makes this feature appear in front of our eyes."

The researchers believe the canyon plays an important role in transporting sub-glacial meltwater from the interior of Greenland to the edge of the ice sheet into the ocean. Evidence suggests that before the presence of the ice sheet, as much as 4 million years ago, water flowed in the canyon from the interior to the coast and was a major river system.

"It is quite remarkable that a channel the size of the Grand Canyon is discovered in the 21st century below the Greenland ice sheet," said Studinger. "It shows how little we still know about the bedrock below large continental ice sheets."

The IceBridge campaign will return to Greenland in March 2014 to continue collecting data on land and sea ice in the Arctic using a suite of instruments that includes ice-penetrating radar.

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