Tuesday, February 1, 2011

ROBOTIC GHOST KNIFEFISH IS BORN

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Researchers at Northwestern University have created a robotic fish that can move from swimming forward and backward to swimming vertically almost instantaneously by using a sophisticated, ribbon-like fin.

The robot -- created after observing and creating computer simulations of the black ghost knifefish -- could pave the way for nimble robots that could perform underwater recovery operations or long-term monitoring of coral reefs.

Led by Malcolm MacIver, associate professor of mechanical and biomedical engineering at Northwestern’s McCormick School of Engineering and Applied Science, the team’s results are published in the Journal of the Royal Society Interface.

The black ghost knifefish, which works at night in rivers of the Amazon basin, hunts for prey using a weak electric field around its entire body and moves both forward and backward using a ribbon-like fin on the underside of its body.

MacIver, a robotics expert who served as a scientific consultant for “Tron: Legacy” and is science advisor for the television series “Caprica,” has studied the knifefish for years. Working with Neelesh Patankar, associate professor of mechanical engineering and co-author of the paper, he has created mechanical models of the fish in hopes of better understanding how the nervous system sends messages throughout the body to make it move.

Planning for the robot -- called GhostBot -- began when graduate student Oscar Curet, a co-author of the paper, observed a knifefish suddenly moving vertically in a tank in MacIver’s lab.

“We had only tracked it horizontally before,” said MacIver, a recent recipient of the prestigious Presidential Early Career Award for Scientists and Engineers. “We thought, ‘How could it be doing this?’”

Further observations revealed that while the fish only uses one traveling wave along the fin during horizontal motion (forward or backward depending on the direction on the wave), while moving vertically it uses two waves. One of these moves from head to tail, and the other moves tail to head. The two waves collide and stop at the center of the fin.

The team then created a computer simulation that showed that when these “inward counterpropagating waves” are generated by the fin, horizontal thrust is canceled and the fluid motion generated by the two waves is funneled into a downward jet from the center of the fin, pushing the body up. The flow structure looks like a mushroom cloud with an inverted jet.

“It’s interesting because you’re getting force coming off the animal in a completely unexpected direction that allows it to do acrobatics that, given its lifestyle of hunting and maneuvering among tree roots, makes a huge amount of sense,” MacIver said.

The group then hired Kinea Design, a design firm founded by Northwestern faculty that specializes in human interactive mechatronics, and worked closely with its co-founder, Michael Peshkin, professor of mechanical engineering, to design and build a robot. The company fashioned a forearm-length waterproof robot with 32 motors giving independent control of the 32 artificial fin rays of the lycra-covered artificial fin. (That means the robot has 32 degrees of freedom. In comparison, industrial robot arms typically have less than 10.) Seven months and $200,000 later, the GhostBot came to life.

The group took the robot to Harvard University to test it in a flow tunnel in the lab of George V. Lauder, professor of ichthyology and co-author of the paper. The team measured the flow around the robotic fish by placing reflective particles in the water, then shining a laser sheet into the water. That allowed them to track the flow of the water by watching the particles, and the test showed the water flowing around the biomimetic robot just as computer simulations predicted it would.

“It worked perfectly the first time,” MacIver said. “We high-fived. We had the robot in the real world being pushed by real forces.”

The robot is also outfitted with an electrosensory system that works similar to the knifefish’s, and MacIver and his team hope to next improve the robot so it can autonomously use its sensory signals to detect an object and then use its mechanical system to position itself near the object.

Humans excel at creating high-speed, low-maneuverability technologies, like airplanes and cars, MacIver said. But studying animals provides a platform for creating low-speed, high-maneuverability technologies -- technologies that don’t currently exist. Potential applications for such a robot include underwater recovery operations, such as plugging a leaking oil pipe, or long-term monitoring of oceanic environments, such as fragile coral reefs.

While the applied work on the robot moves ahead in the lab, the group is pursuing basic science questions as well. “The robot is a tool for uncovering the extremely complicated story of how to coordinate movement in animals,” MacIver said. “By simulating and then performing the motions of the fish, we’re getting insight into the mechanical basis of the remarkable agility of a very acrobatic, non-visual fish. The next step is to take the sensory work and unite the two.”

Northwestern University

BREAKTHROUGH IN CONVERTING HEAT WASTE TO ELECTRICITY

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Researchers at Northwestern University have placed nanocrystals of rock salt into lead telluride, creating a material that can harness electricity from heat-generating items such as vehicle exhaust systems, industrial processes and equipment and sun light more efficiently than scientists have seen in the past.

The material exhibits a high thermoelectric figure of merit that is expected to enable 14 percent of heat waste to electricity, a scientific first. Chemists, physicists and material scientists at Northwestern collaborated to develop the material. The results of the study are published by the journal Nature Chemistry.

“It has been known for 100 years that semiconductors have this property that can harness electricity,” said Mercouri Kanatzidis, the Charles E. and Emma H. Morrison Professor of Chemistry in The Weinberg College of Arts and Sciences. “To make this an efficient process, all you need is the right material, and we have found a recipe or system to make this material.”

Kanatzidis, co-author of the study, and his team dispersed nanocrystals of rock salt (SrTe) into the material lead telluride (PbTe). Past attempts at this kind of nanoscale inclusion in bulk material have improved the energy conversion efficiency of lead telluride, but the nano inclusions also increased the scattering of electrons, which reduced overall conductivity. In this study, the Northwestern team offers the first example of using nanostructures in lead telluride to reduce electron scattering and increase the energy conversion efficiency of the material.

“We can put this material inside of an inexpensive device with a few electrical wires and attach it to something like a light bulb,” said Vinayak Dravid, professor of materials science and engineering at Northwestern’s McCormick School of Engineering and Applied Science and co-author of the paper. “The device can make the light bulb more efficient by taking the heat it generates and converting part of the heat, 10 to 15 percent, into a more useful energy like electricity.”

The automotive, chemical, brick, glass and any industry that uses heat to make products could make their system more efficient with the use of this scientific breakthrough, said Kanatzidis, who also has a joint appointment at the Argonne National Laboratory.

“The energy crisis and the environment are two major reasons to be excited about this discovery, but this could just be the beginning,” Dravid said. “These types of structures may have other implications in the scientific community that we haven’t thought of yet, in areas such as mechanical behavior and improving strength or toughness. Hopefully others will pick up this system and use it.”

(Photo: Northwestern University)

Northwestern University

RESEARCH SHOWS WHEN STEM CELL DESCENDANTS LOSE THEIR VERSATILITY

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Stem cells are the incomparably versatile progenitors of every cell in our body. Some maintain this remarkable plasticity throughout the life of an animal, prepared to respond as needed to repair an injury, for instance. Others differentiate into specialized cells, regenerating tissue or facilitating some other process before dying.

Now new research from Rockefeller University defines the point at which hair follicle stem cells abandon their trademark versatility, or “stemness,” having left their niche to make new hairs. It also shows how these fated stem cell descendants then regulate the activity of their forebears.

“We and others have been focusing on what mobilizes stem cells to make tissue,” says Elaine Fuchs, Rebecca C. Lancefield Professor and head of the Laboratory of Mammalian Cell Biology and Development. “However, it is just as important for stem cells to know when to stop the process, which is what we’ve found here.”

The researchers, led by Ya-Chieh Hsu, a postdoctoral associate in Fuchs’ lab, focused on mouse hair follicles, which undergo cyclical bouts of growth, destruction and rest, a process requiring the activation of stem cells. Stem cells are usually inactive, at rest in their niche, but when activated, they proliferate and leave that niche to make new hairs. In the new research, published last week by Cell, the researchers drilled down on this cycle, defining the point at which activated stem cells become irreversibly committed to becoming the specialized cells needed to grow hair.

Through gene expression analysis and experiments designed to test the cells’ function at different stages in the cycle, the researchers show that early stem cell descendents can retain their stemness and return back to their niche when hair growth stops. In fact, even after their proliferating descendants irreversibly lose their stemness, some can still find their way back to the niche, where they continue to serve two primary purposes: they hold the hairs tightly in place to prevent hair loss, and they release inhibitory signals that prevent the stem cells from activating too early.

“This study shows that committed stem cell descendents transmit inhibitory signals back to the stem cells and return them to a dormant state,” says Fuchs, who is also a Howard Hughes Medical Institute investigator. “The finding gives us new insights into why our spurts of hair growth are followed by a resting period. For many tissues of the body, such negative feedback loops could provide the necessary signals to prevent tissue overgrowth.”

These findings is work represents a new concept in stem cell biology — that an irreversibly committed cell that is downstream in a stem cell lineage can become an essential regulator of stem cells, the researchers say. In other words, the children tell the parents how to behave. “In many systems, stem cells and their differentiated progeny coexist in close proximity,” Hsu says. “The ability of the progeny to regulate stem cell activity could be a general but previously unrecognized phenomenon which enables stem cells to know when to stop making tissue.”

(Photo: Rockefeller University)

Rockefeller University

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