Snake robots learn to turn by following the lead of real sidewinders

Howie Choset, professor at CMU’s Robotics Institute, said by learning from real sidewinders, researchers can make snake robots much more valuable as tools for urban search-and-rescue tasks, power plant inspections and even archaeological exploration

Researchers at Carnegie Mellon University who develop snake-like robots have picked up a few tricks from real sidewinder rattlesnakes on how to make rapid and even sharp turns with their undulating, modular device.

Working with colleagues at the Georgia Institute of Technology and Zoo Atlanta, they have analyzed the motions of sidewinders and tested their observations on CMU's snake robots. They showed how the complex motion of a sidewinder can be described in terms of two wave motions -- vertical and horizontal body waves -- and how changing the phase and amplitude of the waves enables snakes to achieve exceptional maneuverability.
"We've been programming snake robots for years and have figured out how to get these robots to crawl amidst rubble and through or around pipes," said Howie Choset, professor at CMU's Robotics Institute. "By learning from real sidewinders, however, we can make these maneuvers much more efficient and simplify user control. This makes our modular robots much more valuable as tools for urban search-and-rescue tasks, power plant inspections and even archaeological exploration."
Their findings are being published this week in the Proceedings of the National Academy of Sciences Early Edition.
The work is a continuation of a collaboration between Howie Choset, CMU professor of robotics, Daniel Goldman, a Georgia Tech associate professor of physics, and Joseph Mendelson III, director of research at Zoo Atlanta. An earlier study, published on Oct. 10, 2014, in the journal Science, analyzed the ability of sidewinders to quickly climb sandy slopes. It showed that despite the snake's hundreds of body elements and thousands of muscles, the sidewinding motion could be simply modeled as a combination of a vertical and horizontal body wave.
With the model in hand and with a method to measure the movements of living snakes, the team, led by Henry Astley, a postdoctoral researcher in Goldman's group, was able to observe that sidewinders make gradual changes in direction by altering the horizontal wave while keeping the vertical wave constant. They also discovered that making a large phase shift in the vertical wave enabled the snake to make a sharp turn in the opposite direction.
Applying these controls to the robot allowed the robot to replicate the turns of the snake, while also simplifying control.
"By looking for insights in nature, we were able to dramatically improve the control and maneuverability of the robot," Astley said, "while at the same time using the robot as a tool to test the theorized control mechanisms of biological sidewinders."
The modular snake robot used in this study was specifically designed to pass horizontal and vertical waves through its body to move in three-dimensional spaces. The robot is two inches in diameter and 37 inches long; its body consists of 16 joints, each joint arranged perpendicular to the previous one. That allows it to assume a number of configurations and to move using a variety of gaits -- some similar to those of a biological snake.

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The above story is based on materials provided by Carnegie Mellon University. Note: Materials may be edited for content and length.

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Journal Reference:

1. Henry C. Astley, Chaohui Gong, Jin Dai, Matthew Travers, Miguel M. Serrano, Patricio A. Vela, Howie Choset, Joseph R. Mendelson III, David L. Hu, and Daniel I. Goldman. Modulation of orthogonal body waves enables high maneuverability in sidewinding locomotion. PNAS, March 23, 2015 DOI: 10.1073/pnas.1418965112

Magnets can control heat and sound

Researchers at The Ohio State University have discovered how to control heat with a magnetic field. An experiment proved that the phonon—the elementary particle that carries heat and sound—has magnetic properties. This artist’s rendering, based on computer simulations, depicts a phonon heating solid material. Atoms of the material, shown in orange, are joined with flexible atomic bonds, shown as springs. The phonon imparts heat by colliding with the center atom, creating a vibration in the springs. The trail of the passing phonon is marked with increased magnetic field intensity, shown in green. The figure in the lower right shows the direction of the applied magnetic field. The researchers found that a sufficiently strong magnetic field can cause phonons to collide with each other and be deflected off-course, which slows the flow of heat through the material

Researchers at The Ohio State University have discovered how to control heat with a magnetic field.

In the March 23 issue of the journal Nature Materials, they describe how a magnetic field roughly the size of a medical MRI reduced the amount of heat flowing through a semiconductor by 12 percent.
The study is the first ever to prove that acoustic phonons -- the elemental particles that transmit both heat and sound -- have magnetic properties.
"This adds a new dimension to our understanding of acoustic waves," said Joseph Heremans, Ohio Eminent Scholar in Nanotechnology and professor of mechanical engineering at Ohio State. "We've shown that we can steer heat magnetically. With a strong enough magnetic field, we should be able to steer sound waves, too."
People might be surprised enough to learn that heat and sound have anything to do with each other, much less that either can be controlled by magnets, Heremans acknowledged. But both are expressions of the same form of energy, quantum mechanically speaking. So any force that controls one should control the other.
"Essentially, heat is the vibration of atoms," he explained. "Heat is conducted through materials by vibrations. The hotter a material is, the faster the atoms vibrate.
"Sound is the vibration of atoms, too," he continued. "It's through vibrations that I talk to you, because my vocal chords compress the air and create vibrations that travel to you, and you pick them up in your ears as sound."
The name "phonon" sounds a lot like "photon." That's because researchers consider them to be cousins: Photons are particles of light, and phonons are particles of heat and sound. But researchers have studied photons intensely for a hundred years -- ever since Einstein discovered the photoelectric effect. Phonons haven't received as much attention, and so not as much is known about them beyond their properties of heat and sound.
This study shows that phonons have magnetic properties, too.
"We believe that these general properties are present in any solid," said Hyungyu Jin, Ohio State postdoctoral researcher and lead author of the study.
The implication: In materials such as glass, stone, plastic -- materials that are not conventionally magnetic -- heat can be controlled magnetically, if you have a powerful enough magnet. The effect would go unnoticed in metals, which transmit so much heat via electrons that any heat carried by phonons is negligible by comparison.
There won't be any practical applications of this discovery any time soon: 7-tesla magnets like the one used in the study don't exist outside of hospitals and laboratories, and the semiconductor had to be chilled to -450 degrees Fahrenheit (-268 degrees Celsius) -- very close to absolute zero -- to make the atoms in the material slow down enough for the phonons' movements to be detectible.
That's why the experiment was so difficult, Jin said. Taking a thermal measurement at such a low temperature was tricky. His solution was to take a piece of the semiconductor indium antimonide and shape it into a lopsided tuning fork. One arm of the fork was 4 mm wide and the other 1 mm wide. He planted heaters at the base of the arms.
The design worked because of a quirk in the behavior of the semiconductor at low temperatures. Normally, a material's ability to transfer heat would depend solely on the kind of atoms of which it is made. But at very low temperatures, such as the ones used in this experiment, another factor comes into play: the size of the sample being tested. Under those conditions, a larger sample can transfer heat faster than a smaller sample of the same material. That means that the larger arm of the tuning fork could transfer more heat than the smaller arm.
Heremans explained why.
"Imagine that the tuning fork is a track, and the phonons flowing up from the base are runners on the track. The runners who take the narrow side of the fork barely have enough room to squeeze through, and they keep bumping into the walls of the track, which slows them down. The runners who take the wider track can run faster, because they have lots of room.
"All of them end up passing through the material -- the question is how fast," he continued. "The more collisions they undergo, the slower they go."
In the experiment, Jin measured the temperature change in both arms of the tuning fork and subtracted one from the other, both with and without a 7-tesla magnetic field turned on.
In the absence of the magnetic field, the larger arm on the tuning fork transferred more heat than the smaller arm, just as the researchers expected. But in the presence of the magnetic field, heat flow through the larger arm slowed down by 12 percent.
So what changed? Heremans said that the magnetic field caused some of the phonons passing through the material to vibrate out of sync so that they bumped into one another, an effect identified and quantified through computer simulations performed by Nikolas Antolin, Oscar Restrepo and Wolfgang Windl, all of Ohio State's Department of Materials Science and Engineering.
In the larger arm, the freedom of movement worked against the phonons -- they experienced more collisions. More phonons were knocked off course, and fewer -- 12 percent fewer -- passed through the material unscathed.
The phonons reacted to the magnetic field, so the particles must be sensitive to magnetism, the researchers concluded. Next, they plan to test whether they can deflect sound waves sideways with magnetic fields.
Co-authors on the study included Stephen Boona, a postdoctoral researcher in mechanical and aerospace engineering; and Roberto Myers, an associate professor of materials science and engineering, electrical and computer engineering and physics.
Funding for the study came from the U.S. Army Research Office, the U.S. Air Force Office of Scientific Research and the National Science Foundation (NSF), including funds from the NSF Materials Research Science and Engineering Center at Ohio State. Computing resources were provided by the Ohio Supercomputer Center.

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Story Source:
The above story is based on materials provided by Ohio State University. The original article was written by Pam Frost Gorder. Note: Materials may be edited for content and length.

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Journal Reference:

1. Hyungyu Jin, Oscar D. Restrepo, Nikolas Antolin, Stephen R. Boona, Wolfgang Windl, Roberto C. Myers, Joseph P. Heremans. Phonon-induced diamagnetic force and its effect on the lattice thermal conductivity. Nature Materials, 2015; DOI: 10.1038/nmat4247

Have researchers discovered the sound of the stars?

Solar flares on our nearest star, the sun.

A chance discovery by a team of researchers, including a University of York scientist, has provided experimental evidence that stars may generate sound.

The study of fluids in motion -- now known as hydrodynamics -- goes back to the Egyptians, so it is not often that new discoveries are made. However when examining the interaction of an ultra-intense laser with a plasma target, the team observed something unexpected.
Scientists including Dr John Pasley, of the York Plasma Institute in the Department of Physics at York, realized that in the trillionth of a second after the laser strikes, plasma flowed rapidly from areas of high density to more stagnant regions of low density, in such a way that it created something like a traffic jam. Plasma piled up at the interface between the high and low density regions, generating a series of pressure pulses: a sound wave.
However, the sound generated was at such a high frequency that it would have left even bats and dolphins struggling! With a frequency of nearly a trillion hertz, the sound generated was not only unexpected, but was also at close to the highest frequency possible in such a material -- six million times higher than that which can be heard by any mammal!
Dr Pasley, who worked with scientists from the Tata Institute of Fundamental Research in Mumbai, India, and the Science and Technology Facilities Council's Central Laser Facility in Oxfordshire, said: "One of the few locations in nature where we believe this effect would occur is at the surface of stars. When they are accumulating new material stars could generate sound in a very similar manner to that which we observed in the laboratory -- so the stars might be singing -- but, since sound cannot propagate through the vacuum of space, no one can hear them."
The technique used to observe the sound waves in the lab works very much like a police speed camera. It allows the scientists to accurately measure how fluid is moving at the point that is struck by the laser on timescales of less than a trillionth of a second.
Dr Alex Robinson from the Plasma Physics Group at STFC's Central Laser Facility developed a numerical model to generate acoustic waves for the experiment. He said, "It was initially hard to determine the origin of the acoustic signals, but our model produced results that compared favorably with the wavelength shifts observed in the experiment. This showed that we had discovered a new way of generating sound from fluid flows. Similar situations could occur in plasma flowing around stars"
The research was funded by the Engineering and Physical Sciences Research Council and the Tata Institute of Fundamental Research. It is published in Physical Review Letters.

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The above story is based on materials provided by University of York. Note: Materials may be edited for content and length.

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Journal Reference:

1. Amitava Adak, A. P. L. Robinson, Prashant Kumar Singh, Gourab Chatterjee, Amit D. Lad, John Pasley, G. Ravindra Kumar. Terahertz Acoustics in Hot Dense Laser Plasmas. Physical Review Letters, 2015; 114 (11) DOI: 10.1103/PhysRevLett.114.115001

One step closer to low cost solar cells

The flexible transparent electrode - “Flextrode.”

The dwindling resources for conventional energy sources make renewable energy an exciting and increasingly important avenue of research. However, even seemingly new and green forms of energy production, like silicon-based solar cells, are not as cost effective as they could be. An OIST research team led by Yabing Qi is investigating solar cells based on organic materials that have electrodes both flexible and transparent, enabling the fabrication of these solar cells at a low cost.

In a recent paper published in the journal Organic Electronics, Qi and his research group characterized the electrodes made with new materials, including plastic, conductive material and zinc oxide. They also successfully identified methods by which to clean the electrodes to restore their conductivity and work function after an extended period of storage, thus contributing to the optimization of making these new solar cells.
Traditional silicon-based solar cells are expensive to make because of the cost of the raw materials and stringent fabrication requirements. Silicon-based solar cells are also rigid and opaque, meaning their usage and placement are limited. Qi and colleagues work with flexible conductive materials that are also transparent. The fabrication of the "Flextrodes," as these flexible transparent electrodes have been named, is more cost effective and potentially easier to fabricate using a method called roll-to-roll coating, due to their flexible nature. For example, the main component for fabricating Flextrodes is PET, the same inexpensive and readily available plastic that comprises disposable drink bottles. In addition, their use and placement is potentially much more diverse than the silicon cells. For example, they may even be placed on windows since the organic solar cells can be made partially transparent.
Since these Flextrodes are a relatively new technology, basic surface science studies had not been conducted. In their recent paper, Qi and colleagues looked at their work function, surface conductivity and chemical states. They also observed that after an extended period of storage, Flextrodes had an insulating layer of contaminants on the surface that greatly reduced their efficiency and function. The researchers were able to show that two common cleaning methods, one using UV ozone treatment, the other using oxygen plasma treatment, were both effective in removing the contaminants and restoring function to the Flextrodes in a timely and cost-efficient way. The research demonstrated that these methods could easily be integrated into the solar cell fabrication process to regenerate ready-to-use Flextrodes.
Qi is excited about the future of these low-cost organic solar cells. He explains that unlike conventional silicon-based solar cells, "the organic materials available to make the cells are virtually limitless." His lab is working on design and optimization of these new solar cells. The possibility of this technology being available for widespread public use may be just around the corner. Perhaps the next window decoration you put up will be one composed of organic solar cells, providing not just nice aesthetics, but clean energy as well.
This work was done in collaboration with Plasticphotovoltaics.org and Prof. Frederik C. Krebs and his laboratory at Technical University of Denmark, who kindly provided the Flextrode for this study.

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Story Source:
The above story is based on materials provided by Okinawa Institute of Science and Technology - OIST. Note: Materials may be edited for content and length.

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Journal Reference:

1. Yuichi Kato, Min-Cherl Jung, Michael V. Lee, Yabing Qi. Electrical and optical properties of transparent flexible electrodes: Effects of UV ozone and oxygen plasma treatments. Organic Electronics, 2014; 15 (3): 721 DOI: 10.1016/j.orgel.2014.01.002

Towards 'printed' organic solar cells and LEDs

A flexible organic solar cell from TREASORES project undergoing mechanical testing: the cell is repeatedly flexed to a 25 mm radius whilst monitoring its performance. Such cells have shown lifetimes in excess of 4000 hours

In order to make solar energy widely affordable scientists and engineers all over the world are looking for low-cost production technologies. Flexible organic solar cells have a huge potential in this regard because they require only a minimum amount of (rather cheap) materials and can be manufactured in large quantities by roll-to-roll (R2R) processing. This requires, however, that the transparent electrodes, the barrier layers and even the entire devices be flexible. The EU-funded project "TREASORES" (Transparent Electrodes for Large Area Large Scale Production of Organic Optoelectronic Devices), which started in November 2012 with an overall budget of more than 14 Mio Euro and is led by Empa researcher Frank Nüesch, aims at developing and demonstrating technologies to facilitate R2R production of organic optoelectronic devices such as solar cells and LED lighting panels.

Transparent electrodes with superior performance
The TREASORES project recently completed its mid-term review and has already achieved some major milestones. The international team that comprises researchers from 19 labs and companies from five European countries has, for instance, developed an ultra-thin transparent silver electrode that is cheaper than, and outperforms, currently used indium tin oxide (ITO) electrodes. The researchers could also demonstrate a record efficiency of 7 % for a perovskite-based solar cell using such novel transparent electrodes. What's more, their first fully R2R-produced solar cells already achieved commercially acceptable lifetimes when tested "in the field." The next step, says Nüesch, is to scale up and improve the most promising technologies identified so far, say, to produce barrier materials and transparent electrodes in larger quantities, i.e. in rolls of more than 100 meters in length.
In its second half, the TREASORES project will also continue to develop other promising technologies such as transparent and flexible electrodes based on woven fabrics, nanowires and carbon nanotubes (CNTs). "We are working on the most crucial issues in large-scale organic optoelectronics. Our new low-cost electrode substrates already outperform existing conductive oxide electrodes in many ways," says Nüesch. "But we must further improve the resulting device yields from large-scale production by reducing the defect density of the substrates."
The new materials have been thoroughly tested using special instruments for mechanical, electrical, and optical testing and their performance in practical devices has been characterized e.g. for lifetime and quality of illumination. Silver nanowires were used to produce flexible electrodes with a sheet resistance of below 20 Ohms/square -- a measure for the electrical conductivity of thin films -- and an optical transmission of 80%. Copper nanowires were even better, yielding a sheet resistance of below 10 Ohms/square and an optical transmission of 90% on glass. They clearly outperformed current ITO electrodes, which typically have sheet resistance values of 100 Ohms/square and above for such high transparency. Solar cell devices with an energy conversion efficiency of over 3% have been made on these substrates with copper electrodes. CNT electrode performance likewise made significant progress during the first half of the project, reaching a sheet resistance of 74 Ohms/square with an optical transmission of 90%. The organic solar cells that were produced with these electrodes reached an energy conversion efficiency of 4.5%.
"Ironing" the rough electrode surface
All these electrode technologies suffer, however, to some extent from waviness or roughness and require a flattening layer to allow defect-free deposition of optoelectronic device stacks. That's why the researchers set out to develop yet another electrode technology, which uses thin silver (Ag) films sandwiched between two metal oxide (MO) layers. These films turned out to be much flatter. MO/Ag/MO electrode stacks provide a sheet resistance of 6 Ohms/square with an optical transmission of 85% and allowed the construction of more efficient optoelectronic devices compared to the other electrode technologies, which is due, at least in part, to the low peak-to-valley roughness of about 20 nm. With these "ultra-flat" electrodes record efficiencies of up to 7% were obtained for organic solar cells using commercially available materials for light harvesting. Using the very same electrode materials, the team achieved 17 lm/W for the production of white light organic LEDs (OLEDs) and more than 20 lm/W for organic light-emitting electrochemical cells (OLECs). Although not quite record values for flexible OLED and OLEC devices, Nüesch stressed that "all electrodes were produced by an R2R process in an industrial environment or with industrially relevant processes on large areas of the polymer substrate. We can thus say that the processes we used are robust and reproducible."

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The above story is based on materials provided by Empa Swiss Federal Laboratories for Materials Science and Technology. Note: Materials may be edited for content and length.

Scientists discover gecko secret: How geckos stay clean even in dusty deserts

In a world first, a research team including James Cook University scientists has discovered how geckos manage to stay clean, even in dusty deserts.

The process, described in Interface, a journal of the Royal Society, may also turn out to have important human applications.
JCU's Professor Lin Schwarzkopf said the group found that tiny droplets of water on geckos, for instance from condensing dew, come into contact with hundreds of thousands of extremely small hair-like spines that cover the animals' bodies.
"If you have seen how drops of water roll off a car after it is waxed, or off a couch that's had protective spray used on it, you've seen the process happening," she said. "The wax and spray make the surface very bumpy at micro and nano levels, and the water droplets remain as little balls, which roll easily and come off with gravity or even a slight wind."
The geckos' hair-like spines trap pockets of air and work on the same principle, but have an even more dramatic effect. Through a scanning electron microscope, tiny water droplets can be seen rolling into each other and jumping like popcorn off the skin of the animal as they merge and release energy.
Scientists were aware that hydrophobic surfaces repelled water, and that the rolling droplets helped clean the surfaces of leaves and insects, but this is the first time it has been documented in a vertebrate animal.
Box-patterned geckos live in semi-arid habitats, with little rain, but may have dew forming on them when the temperature drops overnight. Professor Schwarzkopf said the process may help geckos keep clean, as the water can carry small particles of dust and dirt away from their body.
"They tend to live in dry environments where they can't depend on it raining, and this process keeps them clean," she said.
She said there were possible applications for use in marine-based electronics that have to shed water quickly and for possible "superhydrophobic" clothing that would not get wet or dirty and would never need washing.

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The above story is based on materials provided by James Cook University. Note: Materials may be edited for content and length.

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Journal Reference:

1. G. S. Watson, L. Schwarzkopf, B. W. Cribb, S. Myhra, M. Gellender, J. A. Watson. Removal mechanisms of dew via self-propulsion off the gecko skin. Journal of The Royal Society Interface, 2015; 12 (105): 20141396 DOI: 10.1098/rsif.2014.1396

New clues from the dawn of the solar system

This artist's impression shows a young sun-like star encircled by its planet-forming disk of gas and dust

A research group in the UA Lunar and Planetary Laboratory has found evidence in meteorites that hint at the discovery of a previously unknown region within the swirling disk of dust and gas known as the protoplanetary disk -- which gave rise to the planets in our solar system.

Led by Kelly Miller, a doctoral student in the lab of Dante Lauretta, the principal investigator of NASA's OSIRIS-REx mission, the team has found evidence of minerals within meteorites that formed in an environment that was enhanced in oxygen and sulfur and date from a time before the particles stuck together, or "accreted," to form larger bodies such as asteroids and planets.
Miller will present the data at the 46th Lunar and Planetary Science Conference, which is held March 16-20 in The Woodlands, Texas. The results are in preparation for publication in a journal, but have not been peer-reviewed yet.
The elements that later went on to constitute the major ingredients in life on Earth -- such as carbon, oxygen, nitrogen and hydrogen -- originated as volatile gases in the protoplanetary disk when the solar system was less than 10 million years old, Miller said.
"If we want to understand how those elements contributed to life, we have to understand where they occurred at the time the solar system formed," she said.
Miller and her team study meteorites called chondrites, which are thought to be the most primitive leftovers from the birth and infancy of the solar system about 4.6 billion years ago. They derive their name from their main component -- chondrules, which formed as molten droplets floating in space.
"We think that chondrites represent the earliest building blocks of rocky planets such as Earth, Mars or Venus," Miller said.
Specifically, Miller and her co-workers studied sections about half as thin as a human hair that were cut from R chondrites, a rare type of meteorite so named after the location where the type specimen fell: Rumuruti in Kenya. R chondrites are thought to have formed somewhere between Earth and Jupiter. In one specimen, found in Antarctica, they discovered a new type of building block called sulfide chondrules. The samples were obtained from the U.S. collection of Antarctic meteorites -- a cooperative effort among NASA, the National Science Foundation (NSF) and the Smithsonian Institution.
"Generally, chondrules are made up of minerals rich in silicon, but the chondrules we found in this meteorite are completely different in that they are composed of sulfide minerals," she explained. "This suggests that they formed in a region that was rich in sulfur, and provides evidence for a previously unknown type of environment in the early solar system."
"Our discovery of the sulfide chondrules will help us put a quantifiable number on how much sulfide was enhanced in that region of the protoplanetary disk," Miller added.
Obtaining a better understanding of the distribution of gases in the early solar system has been identified by the Planetary Science Decadal Survey as a primary objective for the study of primitive bodies. Published by the National Research Council for NASA and other government agencies such as the National Science Foundation, the document identifies key questions in planetary science and outlines plans for space- and ground-based exploration ten years into the future.
"What is exciting about this sample is that it has not been heated to high temperatures and thereby altered in its composition," Miller said. "We know it's a fragment of a larger asteroid, and some of that asteroid heated up to higher temperatures, erasing the signature of the original building blocks of the asteroid, but our piece retains the original building blocks."
"These sulfide chondrules help us pin down when and where that sulfur enhancement occurred and help us better understand the process," she added.
To learn more about the early stages of the solar system including the origin of the building blocks of life and water, the UA-led OSIRIS-REx mission is getting ready to launch a robotic spacecraft to asteroid Bennu in 2016 and bring a sample of at least 60 grams of pristine material back to Earth for study. The mission will provide ample amounts of sample material and, most importantly, from a known context.
"Unlike with meteorites that came to us serendipitously and we're lacking the context of where the material formed, with OSIRIS-REx we will know exactly where that piece came from, and we will know the travel history of Bennu -- where it has been in the past," Miller said.

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Story Source:
The above story is based on materials provided by University of Arizona. The original article was written by Daniel Stolte. Note: Materials may be edited for content and length