Thursday, September 10, 2009

ROBOTS SWIM WITH THE FISHES

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Borrowing from Mother Nature, a team of MIT researchers has built a school of swimming robo-fish that slip through the water just as gracefully as the real thing, if not quite as fast.

Mechanical engineers Kamal Youcef-Toumi and Pablo Valdivia Y Alvarado have designed the sleek robotic fish to more easily maneuver into areas where traditional underwater autonomous vehicles can't go. Fleets of the new robots could be used to inspect submerged structures such as boats and oil and gas pipes; patrol ports, lakes and rivers; and help detect environmental pollutants.

"Given the (robotic) fish's robustness, it would be ideal as a long-term sensing and exploration unit. Several of these could be deployed, and even if only a small percentage make it back there wouldn't be a terrible capital loss due to their low cost," says Valdivia Y Alvarado, a recent MIT PhD recipient in mechanical engineering.

Robotic fish are not new: In 1994, MIT ocean engineers demonstrated Robotuna, a four-foot-long robotic fish. But while Robotuna had 2,843 parts controlled by six motors, the new robotic fish, each less than a foot long, are powered by a single motor and are made of fewer than 10 individual components, including a flexible, compliant body that houses all components and protects them from the environment. The motor, placed in the fish's midsection, initiates a wave that travels along the fish's flexible body, propelling it forward.

The robofish bodies are continuous (i.e., not divided into different segments), flexible and made from soft polymers. This makes them more maneuverable and better able to mimic the swimming motion of real fish, which propel themselves by contracting muscles on either side of their bodies, generating a wave that travels from head to tail.

"Most swimming techniques can be copied by exploiting natural vibrations of soft structures," says Valdivia Y Alvarado.

As part of his doctoral thesis, Valdivia Y Alvarado created a model to calculate the optimal material properties distributions along the robot's body to create a fish with the desired speed and swimming motion. The model, which the researchers initially proposed in the journal Dynamic Systems Measurements and Control (ASME), also takes into account the robot's mass and volume. A more detailed model is described in Valdivia Y Alvarado's thesis and will soon be published along with new applications by the group.

Other researchers, including a team at the University of Essex, have developed new generations of robotic fish using traditional assembly of rigid components to replicate the motions of fish, but the MIT team is the only one using controlled vibrations of flexible bodies to mimic biological locomotion.

"With these polymers, you can specify stiffness in different sections, rather than building a robot with discrete sections," says Youcef-Toumi. "This philosophy can be used for more than just fish" - for example, in robotic prosthetic limbs.

With motors in their bellies and power cords trailing as they swim, the robo-fish might not be mistaken for the real thing, but they do a pretty good fish impersonation.

The team's first prototypes, about five inches long, mimic the carangiform swimming technique used by bass and trout. Most of the movement takes place in the tail end of the body. Fish that use this type of motion are generally fast swimmers, with moderate maneuverability.

Later versions of the robo-fish, about eight inches long, swim like tuna, which are adapted for even higher swimming speeds and long distances. In tuna, motion is concentrated in the tail and the peduncle region (where the tail attaches to the body), and the amplitude of body motions in this region is greater than in carangiform fish.

Real fish are exquisitely adapted to moving through their watery environment, and can swim as fast as 10 times their body length per second. So far, the MIT researchers have gotten their prototypes close to one body length per second - much slower than their natural counterparts but faster than earlier generations of robotic fish.

The new robo-fish are also more durable than older models - with their seamless bodies, there is no chance of water leaking into the robots and damaging them. Several four-year-old prototypes are still functioning after countless runs through the testing tank, which is filled with tap water.

Current prototypes require 2.5 to 5 watts of power, depending on the robot's size. That electricity now comes from an external source, but in the future the researchers hope to power the robots with a small internal battery.

Later this fall, the researchers plan to expand their research to more complex locomotion and test some new prototype robotic salamanders and manta rays.

"The fish were a proof of concept application, but we are hoping to apply this idea to other forms of locomotion, so the methodology will be useful for mobile robotics research - land, air and underwater - as well," said Valdivia Y Alvarado.

(Photo: Patrick Gillooly)

MIT

SLOW-MOTION EARTHQUAKE TESTING PROBES HOW BUILDINGS COLLAPSE IN QUAKES

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It takes just seconds for tall buildings to collapse during powerful earthquakes. Knowing precisely what's happening in those seconds can help engineers design buildings that are less prone to sustaining that kind of damage.

But the nature of collapse is not well understood. It hasn't been well-studied experimentally because testing full-scale buildings on shake tables is a massive, expensive and risky undertaking.

That's why researchers at the University at Buffalo and Japan's Kyoto University teamed up recently to try an innovative "hybrid" approach to testing that may provide a safer, far less expensive way to learn about how and why full-scale buildings collapse.

"One of the key issues in earthquake engineering is how much damage structures can sustain before collapsing so people can safely evacuate," explains principal investigator Gilberto Mosqueda, Ph.D., UB assistant professor of civil, structural and environmental engineering. "We don't really know the answer because testing buildings to collapse is so difficult. With this hybrid approach, it appears that we have a safe, economic way to test realistic buildings at large scales to collapse."

The UB/Kyoto team's positive results could enable engineers to significantly improve their understanding of the mechanisms leading to collapse without the limitations of cost, reduced scale and simplified models necessary for shake table testing in the U.S.

In the unusual "slow motion earthquake" test conducted in late July, UB and Kyoto engineers successfully used the hybrid approach (see video at http://seesl.buffalo.edu/projects/hybridmoment/video.asp) to mimic a landmark, full-scale experiment conducted in 2007 on the E-Defense shake table at the Miki City, Japan, facility. In that test (see video of the 2007 test at http://www.youtube.com/watch?v=MV4GcUZyTzo), a four-story steel building was subjected to a simulation of ground motions that occurred during the 1995 Kobe earthquake.

But instead of using a full-scale steel building, this time, the researchers developed a hybrid representation of that test by combining experimental techniques carried out in earthquake engineering labs in Buffalo and Kyoto with numerical simulations conducted over the Internet.

The landmark data from the E-Defense test was used to verify the effectiveness of the hybrid approach. Only the parts of the buildings that were expected to initiate collapse were tested experimentally.

"If this had been a real building, it would have toppled over," says Mosqueda.

That presents a real problem in a laboratory.

"You can't allow a structure to collapse completely on a shake table," he said. "You need to have support mechanisms in place, like scaffolds, to catch the falling structure."

The building in the original full scale test weighed more than 200 tons. That kind of weight puts shake tables under enormous stress, Mosqueda explains. It not only forces them to operate at full capacity, there is the additional potential for the heavy structure to crash down on the equipment.

"But in this case, we simulated the load with high-performance hydraulic actuators so the specimen overall was actually pretty light," explains Mosqueda. "We completely did away with the hazard of having tons of weight overhead that could come crashing down. Here, we just shut off the hydraulics and the load disappeared."

It took the U.S. and Japanese researchers, who were communicating over the Internet, about two hours to subject the hybrid model to the powerful ground motions that represented approximately the first five seconds of the 1995 Kobe quake.

According to Mosqueda, the hybrid test paves the way for additional experiments that will allow researchers to more precisely learn about the nature of structural collapse.

"We want to know, for example, what is the probability that a building will collapse in the next expected earthquake," says Mosqueda. "First, we need to develop this capability to understand and simulate how they collapse. Then we can determine how to improve new construction or retrofit existing buildings so that they are less likely to collapse."

The experimental part of the test involved a half-scale, nine-foot-tall structure in UB's Structural Engineering and Earthquake Simulation Laboratory (SEESL), while a second experimental component was located at Kyoto University. Together, the two experimental substructures represented the first one-and-a-half stories, while numerical simulations represented the rest of the building.

Mosqueda explains that while reduced-scale models were used in this preliminary test to evaluate the method, the capacity exists at UB and other laboratories to apply this approach to full-scale buildings.

(Photo: U. Buffalo)

University at Buffalo

HUMIDITY KEY TO HEALTHY NAILS SUGGESTS NEW RESEARCH

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Natural material scientists and biomechanics experts have joined forces to examine how nails cope with various stresses under different environmental conditions.

Dr Stephen Eichhorn from The School of Materials and Dr Roland Ennos from The Faculty of Life Sciences performed tests on a large number of fingernail clippings provided by healthy young adult volunteers.

Samples were placed into special metal grips under controlled lab conditions and several tests were performed under different levels of humidity.

The results suggest that fingernails resist damage such as splitting and shearing most strongly in environmental conditions of 55 per cent relative humidity.

Researchers report that nails are more brittle when humidity is lower.

They found that at higher levels of humidity nails are more flexible – although they are more susceptible to shearing.

They also found that nails recover their mechanical properties if they are pulled and then relaxed.

It’s thought this is due to changes that occur, when moisture is present, in the material that binds together the fibrous components of the fingernail.

Controlled bending tests showed this material undergoes a dramatic change in its properties at 55 per cent relative humidity, becoming more flexible at higher humidities.

Researchers say this seems to explain why it’s easier for people to cut their nails after a bath or shower – and may give clues to how our nails have evolved for use in ambient conditions.

Dr Roland Ennos said: “The mechanical properties of fingernails are important because of their impact in preventing damage and in maintaining their appearance.

“In particular, knowing the effect of local environmental conditions can tell us how they might best be protected.”

Dr Stephen Eichhorn added: “We have found that fingernails cope remarkably well over a range of humidities, but it is best to not get them completely dry or wet.

“At an average of 55 per cent humidity, which is what you would experience normally, it appears that nails have optimum mechanical properties, and resist bending.”

(Photo: U. Manchester)

University of Manchester

LIGHTNING'S MIRROR IMAGE ... ONLY MUCH BIGGER

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With a very lucky shot, scientists have captured a one-second image and the electrical fingerprint of huge lightning that flowed 40 miles upward from the top of a storm.

These rarely seen, highly charged meteorological events are known as gigantic jets, and they flash up to the lower levels of space, or ionosphere.

While they don't occur every time there is lightning, they are substantially larger than their downward striking cousins.

"Despite poor viewing conditions as a result of a full moon and a hazy atmosphere, we were able to clearly capture the gigantic jet," said study leader Steven Cummer, an electrical and computer engineer at Duke University in North Carolina.

Images of gigantic jets have only been recorded on five occasions since 2001. The Duke University team caught a one-second view and magnetic field measurements that are now giving scientists a much clearer understanding of these rare events.

"This confirmation of visible electric discharges extending from the top of a storm to the edge of the ionosphere provides an important new window on processes in Earth's global electrical circuit," said Brad Smull, program director in NSF's Division of Atmospheric Sciences, which funded the research.

"Our measurements show that gigantic jets are capable of transferring a substantial electrical charge to the lower ionosphere," Cummer said.

"They are essentially upward lightning from thunderclouds that deliver charge just like conventional cloud-to-ground lightning. What struck us was the size of this event."

It appears from the measurements that the amount of electricity discharged by conventional lightning and gigantic jets is comparable, Cummer said.

But the gigantic jets travel farther and faster than conventional lightning because thinner air between the clouds and ionosphere provides less resistance.

Whereas a conventional lightning bolt follows a six-inch channel and travels about 4.5 miles down to earth, the gigantic jet recorded by the scientists contained multiple channels and traveled about 40 miles upward.

"Given that reservoirs of electric charge in thunderstorms are the sources for both lightning and gigantic jets, and that both events involve contact between these reservoirs and a very large conducting surface, it is not surprising that their charge transfers are comparable," Cummer said.

Scientists don't know what conditions or what types of storms are conducive to gigantic jet formation.

It has been difficult in the past to obtain images of gigantic jets because they occur so quickly that cameras have to be trained on them at the precise moment they occur.

Cummer caught the gigantic jet almost by accident.

The equipment had been set to capture another phenomenon known as sprites, which were first photographed in 1989.

Sprites are electrical discharges that occur above storm clouds and are colored red or blue, with jellyfish-like tendrils hanging down.

Cummer maintains a low-light video camera trained to the sky and programmed to start recording when specific meteorological conditions occur.

At the same time, other equipment constantly measures radio emissions in the same sector to capture electrical events. A special GPS system ensures that the readings from all the equipment are synchronized.

Cummer is planning to install a low-light, high-speed camera to capture gigantic jet images in color, which could provide additional information about chemical processes and temperatures inside the phenomenon.

(Photo: Steven Cummer)

National Science Foundation

ULTRATHIN LEDS CREATE NEW CLASSES OF LIGHTING AND DISPLAY SYSTEMS

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A new process for creating ultrathin, ultrasmall inorganic light-emitting diodes (LEDs) and assembling them into large arrays offers new classes of lighting and display systems with interesting properties, such as see-through construction and mechanical flexibility, that would be impossible to achieve with existing technologies.

Applications for the arrays, which can be printed onto flat or flexible substrates ranging from glass to plastic and rubber, include general illumination, high-resolution home theater displays, wearable health monitors, and biomedical imaging devices.

“Our goal is to marry some of the advantages of inorganic LED technology with the scalability, ease of processing and resolution of organic LEDs,” said John Rogers, the Flory-Founder Chair Professor of Materials Science and Engineering at the University of Illinois.

Rogers and collaborators at the U. of I., Northwestern University, the Institute of High Performance Computing in Singapore, and Tsinghua University in Beijing describe their work in the Aug. 21 issue of the journal Science.

Compared to organic LEDs, inorganic LEDs are brighter, more robust and longer-lived. Organic LEDs, however, are attractive because they can be formed on flexible substrates, in dense, interconnected arrays. The researchers’ new technology combines features of both.

“By printing large arrays of ultrathin, ultrasmall inorganic LEDs and interconnecting them using thin-film processing, we can create general lighting and high-resolution display systems that otherwise could not be built with the conventional ways that inorganic LEDs are made, manipulated and assembled,” Rogers said.

To overcome requirements on device size and thickness associated with conventional wafer dicing, packaging and wire bonding methods, the researchers developed epitaxial growth techniques for creating LEDs with sizes up to 100 times smaller than usual. They also developed printing processes for assembling these devices into arrays on stiff, flexible and stretchable substrates.

As part of the growth process, a sacrificial layer of material is embedded beneath the LEDs. When fabrication is complete, a wet chemical etchent removes this layer, leaving the LEDs undercut from the wafer, but still tethered at anchor points.

To create an array, a rubber stamp contacts the wafer surface at selected points, lifts off the LEDs at those points, and transfers them to the desired substrate.

“The stamping process provides a much faster alternative to the standard robotic ‘pick and place’ process that manipulates inorganic LEDs one at a time,” Rogers said. “The new approach can lift large numbers of small, thin LEDs from the wafer in one step, and then print them onto a substrate in another step.”

By shifting position and repeating the stamping process, LEDs can be transferred to other locations on the same substrate. In this fashion, large light panels and displays can be crafted from small LEDs made in dense arrays on a single, comparatively small wafer. And, because the LEDs can be placed far apart and still provide sufficient light output, the panels and displays can be nearly transparent. The thin device geometries allow the use of thin-film processing methods, rather than wire bonding, for interconnects.

In addition to solid-state lighting, instrument panels and display systems, flexible and even stretchable sheets of printed LEDs can be achieved, with potential use in the health-care industry.

“Wrapping a stretchable sheet of tiny LEDs around the human body offers interesting opportunities in biomedicine and biotechnology,” Rogers said, “including applications in health monitoring, diagnostics and imaging.”

(Photo: D. Stevenson and C. Conway, Beckman Institute, University of Illinois)

University of Illinois

LET THERE BE LIGHT: TEACHING MAGNETS TO DO MORE THAN JUST STICK AROUND

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That palm tree magnet commemorating your last vacation is programmed for a simple function -- to stick to your refrigerator. Similarly, semiconductors are programmed to convey bits of information small and large, processing information on your computer or cell phone.

Scientists are working to coax those semiconductors to be more than conveyers, to actually perform some functions like magnets, such as data recording and electronic control. So far most of those effects could only be achieved at very cold temperatures: minus 260 degrees Celsius or more than 400 below zero Fahrenheit, likely too cold for most computer users.

However, researchers led by a University of Washington chemist report in Science that they have been able to train tiny semiconductor crystals, called nanocrystals or quantum dots, to display new magnetic functions at room temperature using light as a trigger.

Silicon-based semiconductor chips incorporate tiny transistors that manipulate electrons based on their charges. Scientists also are working on ways to use electricity to manipulate the electrons' magnetism, referred to as "spin," but are still searching for the breakthrough that will allow "spintronics" to function at room temperature without losing large amounts of the capability they have at frigid temperatures.

The team led by Daniel Gamelin, a UW chemistry professor, has found a way to use photons -- tiny light particles -- to manipulate the magnetism of semiconductor nanocrystals efficiently, even up to room temperature.

"This provides a completely new approach to microelectronics, if you can use spin instead of charge to process information and use photons to manipulate that process," Gamelin said. "It opens the door to materials that store information and perform logic functions at the same time without the need for super cooling."

The team used nanocrystals of a cadmium-selenium semiconductor called cadmium selenide, but replaced some nonmagnetic cadmium ions with magnetic manganese ions. The crystals, smaller than 10 nanometers across (a nanometer is one-billionth of an inch), were then suspended in a colloid solution, like droplets of cream suspended in milk.

Beams of photons were used to align all of the manganese ions' spins, creating magnetic fields as much as 500 times more powerful than in the same semiconductor material without manganese. The magnetic effects were strongest at low temperatures, but remained remarkably strong up to room temperature, Gamelin said.

Besides Gamelin, authors of the Science paper are Rémi Beaulac and Paul Archer of the UW and Lars Schneider and Gerd Bacher of the University of Duisburg-Essen in Germany.

In a second paper published in the online edition of Nature Nanotechnology, Gamelin's group reported related effects in semiconductor nanocrystals made of zinc oxide but also containing small amounts of manganese impurities.

With zinc oxide, photons acted more as an on-off switch -- once photons altered the zinc oxide's magnetism, the photon stream could be removed and the effect remained in place until another stimulus was applied to turn the effect off again.

Besides Gamelin, authors of the Nature Nanotechnology paper are Stefan Ochsenbein, Yong Feng, Kelly Whitaker, Ekaterina Badaeva, William Liu and Xiaosong Li, all of the UW.

Some behaviors described in the papers have been seen previously at very low temperatures, but in those cases the active materials were embedded in other crystals and so could not be isolated or processed. Suspending the nanocrystals in a colloid solution brings the magnetic effects into a new functional form that could be useful for integration with unconventional materials, Gamelin said. For example, the solution containing the crystals could be applied to a film using a device like an ink jet printer, or interfaced with carbon-based materials using techniques not typically practical for magnetic semiconductors.

"We've brought these spin effects into a processable form," he said. "I think both of these papers are converging on the same applications. We're exploring how to manipulate spins in these nanostructures and perhaps opening the door for some exciting new technologies."

University of Washington

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