Thursday, October 29, 2009

TRACKING ICY OBJECTS, ACROSS THE GLOBE

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On any given night, numerous icy bodies orbiting the sun far beyond the orbit of Pluto may happen to pass in front of a star (as seen from Earth). These events are called occultations, but because the icy moon-sized globes called Kuiper Belt Objects are so small, and their orbits not very accurately known, the vast majority of these events will go unobserved.

That's too bad, because there's a lot to be learned by watching occultations: It's a way to learn the exact size of the object, to discover whether it's actually a pair of objects or is accompanied by one or more moons, and whether or not it has an atmosphere. These questions bear directly on our understanding of the origins of our solar system, because Kuiper Belt Object — in a belt of tens of thousands of icy worlds that includes the former planet Pluto — are thought to be the nearly unchanged remnants of the small bodies called planetesimals that slammed together more than 4 billion years ago to form the planets themselves.

Now, an MIT-led group is aiming to pin down predictions of occultations so that they can be observed systematically by teams of observers scattered across the globe. Multiple observations are essential: they allow for the collection of as much data as possible from these events.

The group's first full-scale test of its system took place Thursday night, with at least 25 observing teams all the way from Australia and New Zealand, through Hawaii, and into the continental United States. The teams include both professional and experienced amateur astronomers, as well as at least one MIT graduate students.

James Elliot, a professor in the Department of Earth, Atmospheric and Planetary Sciences, is leading the project, and was due to discuss it and first-look results from Thursday night's observations on Friday at the annual meeting of the American Astronomical Society's Division for Planetary Sciences, being held in Puerto Rico.

Ultimately, the team hopes to be able to produce occultation predictions accurate enough to guide observations by NASA's new airplane-mounted telescope, called Sofia, which is expected to begin scientific work early next year. Thursday's observations were a kind of test case, Elliott says, because "with Sofia, it's going to be such a production, it would be very costly to get it wrong. This will test our ability to get it right."

(Photo: Carlos Zuluaga; courtesy of the Planetary Astronomy Lab)

Massachusetts Institute of Technology

WHY GIANT SEA SCORPIONS GOT SO BIG

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Research on giant sea scorpions (eurypterids) – the largest bugs that ever lived – has shed new light on why eurypterids became so large and eventually died out.

Originally proposed in the 1930s, ‘Romer’s theory’ argues that eurypterids evolved in an ‘arms race’, alongside early vertebrates – giant armour-plated fish called placoderms – which is why they became so large. Subsequently, scientists have thought that eurypterids evolved to their huge size due to higher levels of oxygen in the atmosphere in the past, and other environmental factors.

The new research shows that both views are correct as the two main eurypterid lineages faced different pressures.

The first group – the giant predatory eurypterids that were up to 2.5 metres long and had swimming paddles – became large due to competition with placoderms in line with Romer’s theory. The second group – initially smaller that walked and scavenged on the sea floor – grew to a huge size due to environmental factors.

Previous research had not differentiated between the two lineages, nor tested either theory statistically and thus overlooked the fact that different pressures affected the two groups independently.

The new study, by James Lamsdell and Dr Simon Braddy from the University of Bristol, which is published today in Biology Letters, compared patterns of the size and numbers of different types, of eurypterids and early fishes.

James Lamsdell, lead author on the paper explains: “We found that the evolution of the two main eurypterid lineages was quite different. The giant predatory eurypterids increased in size but decreased in diversity as placoderms become more common, while the other form of eurypterids that were initially small scavengers, only reached their massive size later on when many other invertebrates also increased in size.”

The demise of the giant predatory eurypterids coincided with the appearance of large placoderms around 400 million years ago. Lamsdell and Braddy show there is a peak in their diversity before placoderms appear in the fossil record, then they rapidly decrease in numbers, increasing in size as they do so before they eventually die out 370 million years ago. This suggests that they attained their huge size by competing with early vertebrates such as placoderms, a battle which they eventually lost.

The scavenging eurypterids on the other hand avoided competing with vertebrates and outlasted the placoderms. They also attained massive sizes, reaching almost 2 metres long, but not until 300 million years ago when they had to cope with life in less salty water, where being bigger is better for helping to regulate such things as the chemistry of blood fluids. They died out due to massive changes in the environment, along with 95% of life, during the Permian extinction 260 million years ago.

Dr Simon Braddy added: “This research indicates that ecology and competition with other animals is as important as environmental change in explaining why some bugs were so big in the past. The moral of the story is: if predators don’t get you, the environment will!”

(Photo: Simon Powell)

University of Bristol

NEW VEHICLE CONCEPT WOULD PROTECT CREWS FROM ROADSIDE BOMBS

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A new crew survivability concept that would build military vehicles around a protected personnel compartment and use a sacrificial “blast wedge” to absorb energy from improvised explosive devices could improve safety for the occupants of future light armored patrol vehicles.

Researchers from the Georgia Tech Research Institute (GTRI) have designed and tested the concept, dubbed ULTRA II, for the U.S. Office of Naval Research (ONR). The crew-protection concept builds on an earlier GTRI development for the ONR that evaluated new concepts for light armored vehicles. A blast test conducted with the ULTRA II full-sized crew compartment test article at the Aberdeen Test Center showed that the new concept could protect the vehicle crew from improvised explosions.

“Instead of up-armoring a standard vehicle or modifying an existing drive train, we built a bubble of force protection first and then addressed vehicle mobility,” explained Vince Camp, a GTRI senior research engineer and the project’s principal investigator. “The idea was to emphasize warfighter protection first by starting with design of an improved crew compartment, as opposed to starting with an existing vehicle and trying to add armor.”

The ULTRA II crew compartment was designed to house six persons: a driver and commander facing forward, and two pairs of crew members behind them, each pair facing opposite sides of the vehicle. By putting their backs toward the center of the crew compartment, the concept moves the crew away from the outside walls to reduce the likelihood of injury from side blasts, provides better visibility for the crew to monitor their surroundings, allows blast-resistant seats to be frame-mounted—and facilitates faster egress from the vehicle.

The crew compartment envisioned by GTRI uses a “space frame” constructed of tubular steel—similar to civilian off-road racing vehicles. An armored steel “skin” provides added structure and moderate ballistic and blast protection. Additional armor is bolted onto the frame in a modular way, allowing varying levels of protection that could be easily modified in the field and changed as new high-performance armor concepts are developed.

An integral part of the protection is provided by a sacrificial “blast wedge” bolted onto the bottom of the vehicle. Constructed of welded steel armor, the wedge both deflects energy away from the vehicle and absorbs energy from a blast, performing a function similar to “crumple zones” in modern civilian vehicles.

The design and fabrication of the test article was conducted by personnel in the Aerospace, Transportation and Advanced Systems Laboratory of GTRI. Tests using a heavily-instrumented test article with instrumented dummies simulating the crew showed that the wedge deflected or absorbed nearly 70 percent of the energy from an explosion beneath it. Damage from the blast was primarily confined to the sacrificial blast wedge and there was no structural damage and no blast penetration to the crew compartment.

“Energy used up in crushing and tearing the metal in the blast wedge is energy that wouldn’t go into injuring the crew,” said Kevin Massey, a GTRI senior research engineer who was part of the project team. “Data from the instrumented dummies shows that had this test been conducted with real warfighters in a real vehicle, we wouldn’t have seen any spinal injuries, head trauma, neck trauma or leg injuries.”

Because the wedge is removable, it could be replaced if damaged. Making the blast wedge removable also allows for an overall reduction of the vehicle’s height for shipping, an important issue for rapid deployment.

The research team, which also included Burt Jennings, Cal Jameson, Jake Leverett and Mark Entrekin, combined non-linear dynamic blast simulations and neural networks to study how blast forces would affect the vehicle. Conventional finite element analysis also provided valuable design feedback in development of the ULTRA II test article.

There were many tradeoffs to consider in designing the new concept, including vehicle height and resistance to blast forces that may come from many different angles.

“To survive the blast, you want to get as high off the ground as possible,” Massey noted. “But the higher you are off the ground, the more likely you are to roll over. This is an example of the tradeoffs that have to be balanced.”

In addition to crew protection, the researchers also designed a translating door that would provide a large side opening similar to that of existing civilian minivans. Such a door system would provide improved ingress/egress for the crew and could remain open when the vehicle is moving.

GTRI has presented data from the test to the Office of Naval Research, and hopes to pursue additional refinements to the blast wedge and overall vehicle concept. Among the goals would be to improve energy absorption from the blast wedge, and to evaluate whether the crew compartment should separate from the drive train in certain types of blasts.

“We think that the concept of a space-frame design is a very viable one, and we want to take the lessons we’ve learned so far to improve on it,” Massey added. “We’d also like to see if the concept of the energy-absorbing wedge can be applied to existing vehicles that are already out there. The bottom line is saving people’s lives and protecting them from injury.”

(Photo: GTRI)

Georgia Tech Research Institute (GTRI)

BY SIMULATING GULLIES, GEOGRAPHERS DISCOVER WAYS TO TAME SOIL EROSION

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Dead zones in critical waterways, accelerated loss of arable land and massive famines. They're all caused by the 24 billion tons of soil that are lost every year to erosion, a phenomenon that costs the world as much as $40 billion annually.

But predicting where erosion occurs, and thus how to prevent it, is a serious challenge.

That's why University at Buffalo geographer Sean Bennett has constructed various systems to model it, with assistance from UB's machine shop. His methods range from the deceptively low-tech, like simulating rainstorms over sandboxes to the high-tech, such as the use of particle image velocimetry (PIV) in large, re-circulating flumes to study how water and grains of sand interact.

The purpose of his work is both exceedingly practical -- geared toward helping farmers learn how to best prevent erosion -- and fundamental, to better understand how planetary surfaces evolve over time.

"We have feet in two domains," he explains, "we're studying processes similar to those that created Niagara Falls; at the same time, we're studying how these processes degrade soil resources worldwide."

The UB research is helping scientists better understand some of the key triggers of erosion, the complex formation of channels on the landscape, called rills and gullies.

"Rills and gullies are the dominant erosion processes on agricultural landscapes today and the main contributor to soil loss," says Bennett, PhD, UB professor of geography in the College of Arts and Sciences and an active researcher in the UB 2020 Strategic Strength in Extreme Events.

Rills and gullies also are a primary cause behind excess sediment and nutrients in waterways, which transports soil and chemicals further downstream.

Bennett says that these high nutrient loadings of nitrogen and phosphorus from eroding agricultural areas destroy aquatic resources, causing unmitigated growth of aquatic algae, depletion of dissolved oxygen and the creation of "dead zones" in places like the Gulf of Mexico.

Ironically, past research by Bennett demonstrated that when farmers till fields to remove rills and gullies, they actually end up accelerating erosion.

"Our numerical model showed that you could reduce soil losses by 400 percent if you adopt a no-till farming practice," says Bennett. "This is because the gullies grow to some maximum size on the landscape during a growing season. If farmers repair them by tilling the soil each spring, the practice actually causes much greater soil loss over the long term."

Bennett's physical model showed similar phenomena.

"Our laboratory landscape showed the same thing," he says, "rills grow and evolve in time and space, erosional processes get arrested and reach an endpoint. After that, they don't produce much sediment."

To model how rills and gullies form, Bennett and his students built a rainfall soil erosion facility, erecting a 30-foot by 8-foot flume containing eight tons of soil, which allowed them to monitor their simulated landscape, looking for disturbances in the soil and the creation of rills and gullies.

Using digital cameras positioned directly above the flume, they developed digital elevation models of the topography across the flume, at millimeter-scale accuracy.

"Each set of images represents how the topography evolved at a discrete space and time during the simulated storm," says Bennett.

The images reveal at what point during the rainfall and runoff, phenomena called headcuts -- small intense areas of localized erosion -- begin to carve deep channels into the soil.

"If we can predict where and when these headcuts occur, and develop technology that allows us to control them, then we can greatly improve soil resource management," says Bennett.

Such technologies include runoff diversions, grass barriers and vegetated waterways.

The images also revealed with startling clarity the fractal patterns that the simulated storm created in the landscape.

"Fractal organization is one of the most compelling ideas in science," says Bennett."While I always knew that landscapes had fractal characteristics, I never saw it demonstrated so clearly as when I saw these treelike patterns in the images we took of our rill networks.

To study sediment transport processes in rivers and how particles interact with the turbulent flow, Bennett designed a 30-foot by 2-foot flume channel, which was constructed by the UB machine shop.

In one experiment, the researchers fill the channel with sand and water, flatten the bed, and then turn on the centrifugal pump to initiate sediment movement.

"Once the flow reaches a certain velocity, the entire bed erupts into ripples, created by the instability between the fast-moving fluid overlying the slow-moving sediment," Bennett explains.

"The PIV system can provide us with high-quality images and data right at the bed surface while these bedforms are being created," he continues. "By examining the physics of sediment transport in this way, we can develop improved models for flow and transport in rivers, allowing us to better manage our river systems and aquatic ecology."

Bennett hopes to use these flumes and equipment to expand his research on the interactions between vegetation and river function and form. Such interactions are critical to the process of restoring and stabilizing degraded streams, a primary thrust of the National Science Foundation-funded "Ecosystem Restoration Through Interdisciplinary Exchange" graduate training program at UB, in which Bennett participates through research and training.

(Photo: U. Buffalo)

University at Buffalo

LIKE HUMANS, MONKEYS FALL INTO THE 'UNCANNY VALLEY'

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Princeton University researchers have come up with a new twist on the mysterious visual phenomenon experienced by humans known as the "uncanny valley." The scientists have found that monkeys sense it too.

The uncanny valley, a phrase coined by a Japanese researcher nearly three decades ago, describes that disquieting feeling that occurs when viewers look at representations designed to be as human-like as possible -- whether computer animations or androids -- but somehow fall short.

Movie-goers may not be familiar with the term, but they understand that it is far easier to love the out-of-proportion cartoon figures in the "The Incredibles," for example, than it is to embrace the more realistic-looking characters in "The Polar Express." Viewers, to many a Hollywood director's consternation, are emotionally unsettled by images of artificial humans that look both realistic and unrealistic at the same time.

In an attempt to add to the emerging scientific literature on the subject and answer deeper questions about the evolutionary basis of communication, Princeton University researchers have found that macaque monkeys also fall into the uncanny valley, exhibiting this reaction when looking at computer-generated images of monkeys that are close but less than perfect representations.

"Increased realism does not necessarily lead to increased acceptance," said Asif Ghazanfar, an assistant professor of psychology and the Princeton Neuroscience Institute, who led the research. It is the first such finding in any animal other than human. The paper, co-written by Shawn Steckenfinger, a research specialist in the Princeton's Department of Psychology, appeared in the October Oct. 12 edition of the Proceedings of the National Academy of Sciences.

The work, according to its authors, is significant because it indicates that there is a biological basis for the uncanny valley and supports theories that propose that the brain mechanisms underlying the uncanny valley are evolutionary adaptations. "These data demonstrate that the uncanny valley effect is not unique to humans and that evolutionary hypotheses regarding its origins are tenable," said Ghazanfar.

The uncanny valley hypothesis was introduced by the Japanese roboticist Masahiro Mori in 1970. The "valley" refers to a dip in a graph that charts a human's positive reaction in response to an image on one axis and a robot's human-likeness on another. People like to study other human faces, and they also can enjoy scrutinizing countenances that clearly are not human, such as a doll's or a cartoon figure's. But when an image falls in between -- close to human but clearly not -- it causes a feeling of revulsion.

Experts praised the Princeton report.

"This study makes a significant contribution to existing knowledge of the uncanny valley," said Karl MacDorman, an associate professor in the School of Informatics at Indiana University, who has led important experiments in the fields of android science and computational neuroscience. "The research design is novel, the experiment is carried out with a high degree of rigor, and the results are compelling, important, newsworthy, and support the [hypothesis]."

He believes the results will be of broad interest to scientists and non-scientists, including "ethologists, animal behaviorists, cognitive psychologists of human perception, evolutionary psychologists, primate social cognitive neuroscientists, humanoid roboticists and human character animators."

In the experiments, the monkeys, which normally coo and smack their lips to engage each other, quickly avert their glances and are frightened when confronted by the close-to-real images. When asked to peer at the less close-to-real faces and real faces, however, they viewed them more often and for longer periods.

Despite the widespread acknowledgement of the uncanny valley as a valid phenomenon, there are no clear explanations for it, Ghazanfar said. One theory suggests that it is the outcome of a "disgust response" mechanism that allows humans to avoid disease. Another idea holds that the phenomenon is an indicator of humanity's highly evolved face processing abilities. Some have suggested the corpse-like appearance of some images elicits an innate fear of death. Still others have posited that the response illustrates what is perceived as a threat to human identity.

Ghazanfar said the research is likely to point him in useful directions to further explore these theories.

(Photo: Shawn Steckenfinger)

University of Princeton

SELF-SACRIFICE AMONG STRANGERS HAS MORE TO DO WITH NURTURE THAN NATURE

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Socially learned behavior and belief are much better candidates than genetics to explain the self-sacrificing behavior we see among strangers in societies, from soldiers to blood donors to those who contribute to food banks. This is the conclusion of a study by Adrian V. Bell and colleagues from the University of California Davis in the Oct. 12 edition of Proceedings of the National Academy of Sciences.

Altruism has long been a subject of interest to evolutionary social scientists. Altruism presents them with a difficult line to argue: behaviors that help unrelated people while being costly to the individual and creating a risk for genetic descendants could not likely be favored by evolution, at least by common evolutionary arguments.

The researchers used a mathematical equation, called the Price equation, that describes the conditions for altruism to evolve. This equation motivated the researchers to compare the genetic and the cultural differentiation between neighboring social groups. Using previously calculated estimates of genetic differences, they used the World Values Survey (whose questions are likely to be heavily influenced by culture in a large number of countries) as a source of data to compute the cultural differentiation between the same neighboring groups. When compared they found that the role of culture had a much greater scope for explaining our pro-social behavior than genetics.

In applying their results to ancestral populations, the World Values Survey was less useful. But ancient cultural practices, such as exclusion from the marriage market, denial of the fruits of cooperative activities, banishment and execution happen now as they did then. These activities would have exerted strong selection against genes tending toward antisocial behavior, and presumably in favor of genes that predisposed individuals toward being pro-social rather than anti-social. This would result in the gene-culture coevolution of human prosocial propensities.

Bell is currently continuing his research in Tonga, where he is planning through ethnography to estimate statistically what social learning behaviors people have in general that may explain the distribution of cultural beliefs across the Tongan Islands. He is developing a survey instrument that will help capture people's cultural beliefs and measure the effect of migration on the similarities and differences between populations.

(Photo: Zina Deretsky, National Science Foundation)

National Science Foundation

HERBIVORY DISCOVERED IN A SPIDER

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A jumping spider from Central America eats mostly plants, according to new research.

Spiders were thought to be strictly predators on animals. The spider, Bagheera kiplingi, was described scientifically in the late 1800s, but its vegetarian tendencies were not observed until the 21st century.

"This is the first spider in the world known to deliberately hunt plant parts. It is also the first found to go after plants as a primary food source," said lead author Christopher Meehan.

Meehan, now a doctoral student in the University of Arizona's department of ecology and evolutionary biology, discovered Bagheera kiplingi's herbivory while he was a student at Villanova University in Pennsylvania.

Of the approximately 40,000 species of spiders known, Bagheera kiplingi is the only species known to be primarily herbivorous. Ironically, the vegetarian spider is named after the panther in Rudyard Kipling's "The Jungle Book."

The spider inhabits several species of acacia shrubs involved in a well-known mutualism between the acacias and several species of ants.

The ants live in hollow spines on the plant and drink nectar from glands at the base of each leaf and eat the specialized leaf tips known as Beltian bodies. In return, the ants fiercely guard the plants against most would-be herbivores.

The leaf-tip structures are named after naturalist Thomas Belt, who published a paper about them in the 1800s.

The B. kiplingi spiders are "cheaters" in the ant-acacia system, stealing and eating both nectar and Beltian bodies without helping to defend the plant, according to the researchers. Although the ants actively patrol the plant for intruders, the spiders' excellent eyesight and agility allow them to avoid the plant's ant bodyguards.

The story of the first known vegetarian spider is also a story of cooperation, rather than competition.

Co-author Eric Olson of Brandeis University had discovered herbivory in B. kiplingi in Costa Rica in 2001. In 2007, Meehan independently observed the same behaviors in spiders in Quintana Roo, Mexico, during a course taught by Villanova professor and study co-author Robert Curry. The two research groups subsequently combined efforts to publish the discovery.

Previously, very few spiders had been seen consuming plants at all. Some spiders had been observed occasionally eating nectar and pollen, although the bulk of their diet was insects and other small animals.

To verify the initial observations of the spiders' herbivory, the researchers documented B. kiplingi feeding behavior using high-definition video recordings. The team identified 140 food items of the Mexican spiders and found that more than 90 percent were Beltian bodies.

For the Costa Rican population of B. kiplingi, only 60 percent of the diet was Beltian bodies. Those spiders were seen with animal prey items more often than were the Mexican B. kiplingi.

Curry said, "What surprised us most about discovering this spider's extraordinary ecology was to find it on the ant-acacias. This well-known mutualism has been studied by tropical ecologists for nearly 50 years, yet the spider's role was not noticed until Olson's discovery in 2001.

"We were lucky to find in Mexico an area where the spider is both exceptionally abundant and even more herbivorous than in Costa Rica," he said.

The team also conducted laboratory analyses of the carbon and nitrogen in B. kiplingi spiders, other local spiders, Beltian bodies, and the acacia-dwelling ants.

Analyzing the different forms of nitrogen and carbon in an animal can indicate its trophic level and its food source.

B. kiplingi spiders were more similar in the nitrogen analyses to the herbivorous acacia-ants than to any of the other spiders sampled, suggesting the ants and the B. kiplingi were on the same level in the food chain. In the carbon analysis, which matches animals to their food source, B. kiplingi spiders and Beltian bodies were almost identical.

Collectively, the data show that B. kiplingi spiders, particularly those from Mexico, obtain most of their diet directly or indirectly from the ant-acacia plants.

Meehan and Curry suggest their finding shows that coevolution between an ant and a plant can result in the development of plant structures that may be especially vulnerable to exploitation by third parties that normally focus on completely different kinds of prey.

B. kiplingi also exhibits signs of sociality. The researchers suspect that something about the spider's transition to herbivory has influenced the species' social evolution, a possibility the researchers are continuing to study.

(Photo: Copyright Robert L. Curry)

University of Arizona

GENTLE TOUCH MAY AID MULTIPLE SCLEROSIS PATIENTS

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A team of University of Illinois at Chicago physical therapists report this month in the journal Neurorehabilitation and Neural Repair that persons with multiple sclerosis use excessive force when they are lifting objects. In an earlier finding reported in the journal Clinical Neurophysiology, they reported that regaining control and coordination may be as easy as applying a gentle touch to the affected hand from a finger of the opposite hand.

"We studied how this light touch application changes the way people apply force to an object they want to grip," said Alexander Aruin, professor of physical therapy. The study compared eight adults with multiple sclerosis to eight without the disease, gender-matched and of comparable age. "In each case, the grip force required to lift an object decreased," said Aruin.

He found similar results in an earlier study he did of people with arm weakness caused by a stroke.

Why the simple light finger touch application works so well is not fully understood, but Aruin offers a hypothesis.

"It could be due to auxiliary sensory information from the contra-lateral arm," he said. "When we use our second hand and touch the wrist of the target hand, available information to the central nervous system about the hand-object interaction may increase. Without the touch, the information needed to manipulate an object comes only through vision and sensory input from just the target arm and hand."

Aruin and his colleagues tested subjects griping and lifting a variety of objects that they moved in several different ways, directions and velocities. The gentle finger touch always helped to reduce grip force, making the task easier.

The UIC researcher said he and his colleagues plan to test the approach on those with other neurological and muscular diseases to examine the effects.

"We look forward to developing training and rehabilitation procedures on how to use this," said Aruin. "We know that MS patients are prone to fatigue and muscle weakness. This finding may enable them to perform daily activities more independently to improve their quality of life."

The papers' lead author was Veena Iyengar, a former master's student of Aruin's now at Advocate Lutheran General Hospital in Park Ridge, IL. Other authors were Marcio Santos, a former UIC postdoctoral fellow now at Santa Catarina State University in Brazil, and Michael Ko, a neurologist with Loyola University Chicago's medical center.

University of Illinois

CHEMISTRY TEAM SEEKS TO USE ARTIFICIAL PHOTOSYNTHESIS AND NANOTUBES TO GENERATE HYDROGEN FUEL WITH SUNLIGHT

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A team of four chemists at the University of Rochester have begun work on a new kind of system to derive usable hydrogen fuel from water using only sunlight.

The project has caught the attention of the U.S. Department of Energy, which has just given the team nearly $1.7 million to pursue the design.

"Everybody talks about using hydrogen as a super-green fuel, but actually generating that fuel without using some other non-green energy in the process is not easy," says Kara Bren, professor in the Department of Chemistry. "People have used sunlight to derive hydrogen from water before, but the trick is making the whole process efficient enough to be useful."

Bren and the rest of the Rochester team—Professor of Chemistry Richard Eisenberg, and Associate Professors of Chemistry Todd Krauss, and Patrick Holland—will be investigating artificial photosynthesis, which uses sunlight to carry out chemical processes much as plants do. What makes the Rochester approach different from past attempts to use sunlight to produce hydrogen from water, however, is that the device they are preparing is divided into three "modules" that allow each stage of the process to be manipulated and optimized far more easily than other methods.

The first module uses visible light to create free electrons. A complex natural molecule called a chromophore that plants use to absorb sunlight will be re-engineered to efficiently generate reducing electrons.

The second module will be a membrane suffused with carbon nanotubes to act as molecular wires so small that they are only one-millionth the thickness of a human hair. To prevent the chromophores from re-absorbing the electrons, the nanotube membrane channels the electrons away from the chromophores and toward the third module.

In the third module, catalysts put the electrons to work forming hydrogen from water. The hydrogen can then be used in fuel cells in cars, homes, or power plants of the future.

By separating the first and third modules with the nanotube membrane, the chemists hope to isolate the process of gathering sunlight from the process of generating hydrogen. This isolation will allow the team to maximize the system's light-harvesting abilities without altering its hydrogen-generation abilities, and vice versa. Bren says this is a distinct advantage over other systems that have integrated designs because in those designs a change that enhances one trait may degrade another unpredictably and unacceptably.

Bren says it may be years before the team has a system that clearly works better than other designs, and even then the system would have to work efficiently enough to be commercially viable. "But if we succeed, we may be able to not only help create a fuel that burns cleanly, but the creation of the fuel itself may be clean."

University of Rochester

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