Science: March 2015

Tuesday 24 March 2015

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.

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

Journal Reference:

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.

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.

Journal Reference:

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.

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

Journal Reference:

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

Friday 20 March 2015

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.

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.

Journal Reference:

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."

Story Source:
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.

Wednesday 18 March 2015

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.

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

Journal Reference:

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.

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

Density of lithium storage materials increased

New storage material with (left) and without lithium (right)

An interdisciplinary team of researchers of Karlsruhe Institute of Technology (KIT) and KIT-founded Helmholtz Institute Ulm (HIU) pushes the further development of lithium ion batteries: The researchers developed a new cathode material based on a new storage principle, as a result of which energy storage densities can be increased beyond those of systems known so far. The researchers now present the new material in the journal "Advanced Energy Materials."

The lithium ion battery currently is the most widespread battery technology. It is indispensable for devices, such as laptops, mobile phones or cameras. Current research activities are aimed at reaching higher lithium storage densities in order to increase the amount of energy stored in a battery. Moreover, lithium storage should be quick for energy supply of devices with high power requirements. This requires the detailed understanding of the electrochemical processes and new development of battery components.
The materials used so far are based on intercalation storage of lithium in small cavities (so-called interstitials), in a host structure that usually consists of metal oxides. This method works well, but the storage densities reached are limited, as lithium cannot be packed very densely in the structure. In addition, intercalation storage of more than one lithium ion per formula unit is generally not possible, as the structure then is no longer stable and collapses. It would therefore be desirable to increase the packing density of lithium in the stable structure and to exceed the upper limits reached so far.
A team around Professor Maximilian Fichtner and Dr. Ruiyong Chen of KIT has now presented a new storage principle and a material on this basis, which allows for the reversible storage of 1.8 Li per formula unit. With a material of the composition Li2VO2F, storage capacities of up to 420 mAh/g were measured at a mean voltage of 2.5 V. As a result of the comparably high density of the material, a storage capacity of up to 4600 Wh/L relative to the active material is obtained.
Contrary to the materials used so far, the new system no longer stores lithium at the interstitials, but directly at the lattice sites of a cubic close packed structure. As a result, packing densities are increased significantly.
Surprisingly, the lithium ions are highly mobile in this structure and can be incorporated into the lattice and removed again easily. Vanadium takes up two charges or releases them again, while the lattice as a whole remains stable -- a novelty in such storage materials. The structure has a high defect mobility, such that the lattice can stabilize itself.
"The high stability of the structure at a high defect mobility, associated with a very small volume change of 3 % only -- this is what makes the new system unusual. The storage principle appears to be transferable to other compositions. Using other compounds of similar structure, we presently measure even higher energy densities than for the vanadium-based system," the head of the research team, Maximilian Fichtner, reports.

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

Journal Reference:

Ruiyong Chen, Shuhua Ren, Michael Knapp, Di Wang, Raiker Witter, Maximilian Fichtner, Horst Hahn. Disordered Lithium-Rich Oxyfluoride as a Stable Host for Enhanced Li Intercalation Storage. Advanced Energy Materials, 2015; DOI: 10.1002/aenm.201401814

On pi day, how scientists use this number

Take JPL Education's Pi Day challenge featuring real-world questions about NASA spacecraft -- then tweet your answers to @NASAJPL_Edu using the hashtag #PiDay. Answers will be revealed on March 16.

If you like numbers, you will love March 14, 2015. When written as a numerical date, it's 3/14/15, corresponding to the first five digits of pi (3.1415) -- a once-in-a-century coincidence! Pi Day, which would have been the 136th birthday of Albert Einstein, is a great excuse to eat pie, and to appreciate how important the number pi is to math and science.

Pi is the ratio of circumference to diameter of a circle. Any time you want to find out the distance around a circle when you have the distance across it, you will need this formula.
Despite its frequent appearance in math and science, you can't write pi as a simple fraction or calculate it by dividing two integers (...3, -2, -1, 0, 1, 2, 3...). For this reason, pi is said to be "irrational." Pi's digits extend infinitely and without any pattern, adding to its intrigue and mystery.
Pi is useful for all kinds of calculations involving the volume and surface area of spheres, as well as for determining the rotations of circular objects such as wheels. That's why pi is important for scientists who work with planetary bodies and the spacecraft that visit them.
At NASA's Jet Propulsion Laboratory, Pasadena, California, pi makes a frequent appearance. It's a staple for Marc Rayman, chief engineer and mission director for NASA's Dawn spacecraft. Dawn went into orbit around dwarf planet Ceres on March 6. Rayman uses a formula involving pi to calculate the length of time it takes the spacecraft to orbit Ceres at any given altitude. You can also use pi to think about Earth's rotation.
"On Pi Day, I will think about the nature of a day, as Earth's rotation on its axis carries me on a circle 21,000 miles (34,000 kilometers) in circumference, which I calculated using pi and my latitude," Rayman said.
Steve Vance, a planetary chemist and astrobiologist at JPL, also frequently uses pi. Lately, he has been using pi in his calculations of how much hydrogen might be available for chemical processes, and possibly biology, in the ocean beneath the surface of Jupiter's moon Europa.
"To calculate the hydrogen produced in a given unit area, we divide by Europa's surface area, which is the area of a sphere with a radius of 970 miles (1,561 kilometers)," Vance said.
Luisa Rebull, a research scientist at NASA's Spitzer Science Center at the California Institute of Technology, Pasadena, also considers pi to be important in astronomy. When calculating the distance between stars in a projection of the sky, scientists use a special kind of geometry called spherical trigonometry. That's an extension of the geometry you probably learned in middle school, but it takes place on a sphere rather than a flat plane.
"In order to do these calculations, we need to use formulae, the derivation of which uses pi," she said. "So, this is pi in the sky!"
Make sure to note when the date and time spell out the first 10 digits of pi: 3.141592653. On 3/14/15 at 9:26:53 a.m., it is literally the most perfectly "pi" time of the century -- so grab a slice of your favorite pie, and celebrate math!
For more fun with pi, check out JPL Education's second annual Pi Day challenge, featuring real-world NASA math problems. NASA/JPL education specialists, with input from scientists and engineers, have crafted questions involving pi aimed at students in grades 4 through 11, but open to everyone. Take a crack at them at:
http://www.jpl.nasa.gov/infographics/infographic.view.php?id=11257
Share your answers on Twitter by tweeting to @NASAJPL_Edu with the hashtag #PiDay. Answers will be revealed on March 16 (aka Pi + 2 Day!).
Resources for educators, including printable Pi Day challenge classroom handouts, are available at: www.jpl.nasa.gov/edu/piday2015
Caltech manages JPL for NASA.

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The above story is based on materials provided by NASA/Jet Propulsion Laboratory. Note: Materials may be edited for content and length.

Tuesday 17 March 2015

To save an entire species, all you need is $1. 3 million a year

How much would you pay to save a species from becoming extinct? A thousand dollars, $1 million or $10 million or more? A new study shows that a subset of species -- in this case 841 to be exact -- can be saved from extinction for about $1.3 million per species per year, but only if conservation efforts are put in place immediately to ensure habitat protection and management, according to researchers that include a Texas A&M professor.

The international team of researchers includes scientists from the Max-Planck Odense Center at the University of Southern Denmark, Imperial College of London, Australia's University of Queensland, the American Bird Conservancy, the IUCN SSC Conservation Breeding Specialist Group, the International Species Information System, the World Association of Zoos and Aquariums, and Burak Güneralp, research assistant professor at Texas A&M. The team's work is published in the current issue of Current Biology.
The researchers developed a "conservation opportunity index" using measurable indicators to quantify the possibility of achieving successful conservation of a species, both in its natural habitat and by establishing insurance populations in zoos. They computed the cost of, and opportunities for, conserving 841 species of mammals, reptiles, birds and amphibians listed by the Alliance for Zero Extinction or AZE as restricted to single sites and categorized as Endangered or Critically Endangered on the IUCN Red List.
The total cost: only $1.3 billion per year to safeguard all 841 species, truly a bargain basement price by any standard, the researchers note. Of this, a little over $1.1 billion per year would go towards conserving the species in their natural habitats and the rest for complementary management in zoos. "Although the cost seems high, safeguarding these species is essential if we want to reduce the extinction rate by 2020," said Prof. Hugh Possingham from the University of Queensland.
"When compared to global government spending on other sectors (such as U.S. defense spending, which is more than 500 times greater), an investment in protecting high biodiversity value sites is minor."
"AZE sites are arguably the most irreplaceable category of important biodiversity conservation sites," notes assistant professor Dalia A. Conde, lead author on the paper at the Max-Planck Odense Center at the University of Southern Denmark. "Conservation opportunity evaluations like ours show the urgency of implementing management actions before it is too late. It is imperative to rationally determine actions for species that we found to have the lowest chances of successful habitat and zoo conservation actions."
"Habitat loss and fragmentation caused by human activities including expansion of urban areas is a major factor putting at risk many of the species in the AZE list," adds Güneralp, co-author of the study. There are about 17,000 species that are now threatened with extinction, and there have been five mass extinctions -- including the one that killed the dinosaurs. Because of habitat loss and fragmentation, many scientists believe that we are now living during the sixth mass extinction period.
While the study indicated that 39 percent of the species scored high for conservation opportunities, it also showed that at least 15 AZE species are in imminent danger of extinction given their low conservation opportunity index. This low index is due to one or a combination of different factors such as: high probability of its habitat becoming urbanized, political instability in the site and/or high costs of habitat protection and management.
Additionally, the opportunity of establishing an insurance population in zoos for these 15 species is low, either due to high costs or lack of breeding expertise for the species. "Our exercise gives us hope for saving many highly endangered species from extinction, but actions need to be taken immediately and, for species restricted to one location, an integrative conservation approach is needed," says Prof. John E. Fa of Imperial College.
The paper states the importance of integrating protection of the places these particular species inhabit with complementary zoo insurance population programs. According to Onnie Byers, Chair of the IUCN SSC Conservation Breeding Specialist Group, "The question is not one of protecting a species in the wild or in zoos. The One Plan approach -- effective integration of planning, and the optimal use of limited resources, across the spectrum of management from wild to zoo -- is essential if we are to have a hope of achieving the Aichi Biodiversity Targets."
Nate Flesness, scientific director of the International Species Information System, stresses that "we want to thank the more than 800 zoos in 87 countries which contribute animal and collection data to the International Species Information System, where the assembled global data enables strategic conservation studies like this."
Markus Gusset of the World Association of Zoos and Aquariums added that "Actions that range from habitat protection to the establishment of insurance populations in zoos will be needed if we want to increase the chances of species' survival."

Story Source:
The above story is based on materials provided by Texas A&M University. Note: Materials may be edited for content and length.

Journal Reference:

Dalia A. Conde, Fernando Colchero, Burak Güneralp, Markus Gusset, Ben Skolnik, Michael Parr, Onnie Byers, Kevin Johnson, Glyn Young, Nate Flesness, Hugh Possingham, John E. Fa. Opportunities and costs for preventing vertebrate extinctions. Current Biology, 2015; 25 (6): R219 DOI: 10.1016/j.cub.2015.01.048

New technology may double radio frequency data capacity

CoSMIC (Columbia high-Speed and Mm-wave IC) Lab full-duplex transceiver IC that can be implemented in nanoscale CMOS to enable simultaneous transmission and reception at the same frequency in a wireless radio

A team of Columbia Engineering researchers has invented a technology -- full-duplex radio integrated circuits (ICs) -- that can be implemented in nanoscale CMOS to enable simultaneous transmission and reception at the same frequency in a wireless radio. Up to now, this has been thought to be impossible: transmitters and receivers either work at different times or at the same time but at different frequencies. The Columbia team, led by Electrical Engineering Associate Professor Harish Krishnaswamy, is the first to demonstrate an IC that can accomplish this. The researchers presented their work at the International Solid-State Circuits Conference (ISSCC) in San Francisco on February 25.

"This is a game-changer," says Krishnaswamy. "By leveraging our new technology, networks can effectively double the frequency spectrum resources available for devices like smartphones and tablets."
In the era of Big Data, the current frequency spectrum crisis is one of the biggest challenges researchers are grappling with and it is clear that today's wireless networks will not be able to support tomorrow's data deluge. Today's standards, such as 4G/LTE, already support 40 different frequency bands, and there is no space left at radio frequencies for future expansion. At the same time, the grand challenge of the next-generation 5G network is to increase the data capacity by 1,000 times.
So the ability to have a transmitter and receiver re-use the same frequency has the potential to immediately double the data capacity of today's networks. Krishnaswamy notes that other research groups and startup companies have demonstrated the theoretical feasibility of simultaneous transmission and reception at the same frequency, but no one has yet been able to build tiny nanoscale ICs with this capability.
"Our work is the first to demonstrate an IC that can receive and transmit simultaneously," he says. "Doing this in an IC is critical if we are to have widespread impact and bring this functionality to handheld devices such as cellular handsets, mobile devices such as tablets for WiFi, and in cellular and WiFi base stations to support full duplex communications."
The biggest challenge the team faced with full duplex was canceling the transmitter's echo. Imagine that you are trying to listen to someone whisper from far away while at the same time someone else is yelling while standing next to you. If you can cancel the echo of the person yelling, you can hear the other person whispering.
"If everyone could do this, everyone could talk and listen at the same time, and conversations would take half the amount of time and resources as they take right now," explains Jin Zhou, Krishnaswamy's PhD student and the paper's lead author. "Transmitter echo or 'self-interference' cancellation has been a fundamental challenge, especially when performed in a tiny nanoscale IC, and we have found a way to solve that challenge."
Krishnaswamy and Zhou plan next to test a number of full-duplex nodes to understand what the gains are at the network level. "We are working closely with Electrical Engineering Associate Professor Gil Zussman's group, who are network theory experts here at Columbia Engineering," Krishnaswamy adds. "It will be very exciting if we are indeed able to deliver the promised performance gains."

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The above story is based on materials provided by Columbia University School of Engineering and Applied Science. Note: Materials may be edited for content and length.

Solar cells: Increased pressure creates a happy union

By tailoring the interface between the two sections of a solar cell, A*STAR researchers have produced a high-performance solar cell from the abundant and cheap materials of copper (II) oxide and silicon.

For solar energy to become environmentally friendly and cost effective, the two main components of 'heterojunction' solar cells ― the n- and p-type layers ― need to be fabricated from nontoxic, abundant materials. Copper (II) oxide, also known as cupric oxide, holds promise as a p-type semiconductor since it meets both these criteria and also has an ideal bandgap for absorbing sunlight and a high light absorption.
On paper, copper oxide and silicon are a perfect pair for producing high-performance solar cells. In practice, however, their performance has been disappointing because of the tendency of holes and electrons to recombine in them ― a process known as charge recombination. This recombination limits the production of electricity in a solar cell since it reverses the generation of electrical charges from light. One cause of this problem is the poor quality of the interface between copper oxide and silicon as the result of silicon oxide on the silicon surface.
Now, Goutam Dalapati from the A*STAR Institute of Materials Research and Engineering at Singapore and co-workers have used conventional procedures to produce high-performance solar cells that employ cupric oxide as the p-type material and silicon as the n-type material. They realized this by increasing the pressure during the deposition stage of fabrication, which they found enhances both the crystal and interface quality, thereby reducing the charge recombination rate.
Using a sequence of analytical techniques -- Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy -- they showed that the interface quality was limited by the formation of a copper-rich oxide layer as well as by the production of a silicon oxide layer on silicon surface. Dalapati explains that the team were surprised by the formation of this copper-rich layer as the cupric oxide target contained an equal mix of copper and oxygen. But the scientists also discovered that they could minimize this layer by increasing the pressure during deposition and the annealing time. Using this tactic, the team successfully produced a high-quality solar cell that had a low charge recombination rate.
Dalapati notes that "to develop cost-effective, environmentally friendly photovoltaic devices using Earth-abundant nontoxic cupric oxide, it is essential that we can increase the efficiency further." This is possible, he adds, "by reducing, or even eliminating, the copper-rich interfacial layer and the silicon oxide insulating layer."

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The above story is based on materials provided by The Agency for Science, Technology and Research (A*STAR). Note: Materials may be edited for content and length.

Journal Reference:

Saeid Masudy-Panah, Goutam Kumar Dalapati, K. Radhakrishnan, Avishek Kumar, Hui Ru Tan, Elumalai Naveen Kumar, Chellappan Vijila, Cheng Cheh Tan, DongZhi Chi. p-CuO/n-Si heterojunction solar cells with high open circuit voltage and photocurrent through interfacial engineering. Progress in Photovoltaics: Research and Applications, 2014; DOI: 10.1002/pip.2483

Thursday 12 March 2015

Silk could be new 'green' material for next-generation batteries

Lithium-ion batteries have enabled many of today's electronics, from portable gadgets to electric cars. But much to the frustration of consumers, none of these batteries last long without a recharge. Now scientists report in the journal ACS Nano the development of a new, "green" way to boost the performance of these batteries -- with a material derived from silk.

Chuanbao Cao and colleagues note that carbon is a key component in commercial Li-ion energy storage devices including batteries and supercapacitors. Most commonly, graphite fills that role, but it has a limited energy capacity. To improve the energy storage, manufacturers are looking for an alternative material to replace graphite. Cao's team wanted to see if they could develop such a material using a sustainable source.
The researchers found a way to process natural silk to create carbon-based nanosheets that could potentially be used in energy storage devices. Their material stores five times more lithium than graphite can -- a capacity that is critical to improving battery performance. It also worked for over 10,000 cycles with only a 9 percent loss in stability. The researchers successfully incorporated their material in prototype batteries and supercapacitors in a one-step method that could easily be scaled up, the researchers note.
The authors acknowledge funding from the National Natural Science Foundation of China.

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The above story is based on materials provided by American Chemical Society. Note: Materials may be edited for content and length.

Journal Reference:

Jianhua Hou, Chuanbao Cao, Faryal Idrees, Xilan Ma. Hierarchical Porous Nitrogen-Doped Carbon Nanosheets Derived from Silk for Ultrahigh-Capacity Battery Anodes and Supercapacitors. ACS Nano, 2015; 150225094419006 DOI: 10.1021/nn506394r

Saturn moon's ocean may harbor hydrothermal activity, spacecraft data suggest

This cutaway view of Saturn's moon Enceladus is an artist's rendering that depicts possible hydrothermal activity that may be taking place on and under the seafloor of the moon's subsurface ocean, based on recently published results from NASA's Cassini mission

NASA's Cassini spacecraft has provided scientists the first clear evidence that Saturn's moon Enceladus exhibits signs of present-day hydrothermal activity which may resemble that seen in the deep oceans on Earth. The implications of such activity on a world other than our planet open up unprecedented scientific possibilities.

"These findings add to the possibility that Enceladus, which contains a subsurface ocean and displays remarkable geologic activity, could contain environments suitable for living organisms," said John Grunsfeld, astronaut and associate administrator of NASA's Science Mission Directorate in Washington. "The locations in our solar system where extreme environments occur in which life might exist may bring us closer to answering the question: are we alone in the universe."
Hydrothermal activity occurs when seawater infiltrates and reacts with a rocky crust and emerges as a heated, mineral-laden solution, a natural occurrence in Earth's oceans. According to two science papers, the results are the first clear indications an icy moon may have similar ongoing active processes.
The first paper, published this week in the journal Nature, relates to microscopic grains of rock detected by Cassini in the Saturn system. An extensive, four-year analysis of data from the spacecraft, computer simulations and laboratory experiments led researchers to the conclusion the tiny grains most likely form when hot water containing dissolved minerals from the moon's rocky interior travels upward, coming into contact with cooler water. Temperatures required for the interactions that produce the tiny rock grains would be at least 194 degrees Fahrenheit (90 degrees Celsius).
"It's very exciting that we can use these tiny grains of rock, spewed into space by geysers, to tell us about conditions on -- and beneath -- the ocean floor of an icy moon," said the paper's lead author Sean Hsu, a postdoctoral researcher at the University of Colorado at Boulder.
Cassini's cosmic dust analyzer (CDA) instrument repeatedly detected miniscule rock particles rich in silicon, even before Cassini entered Saturn's orbit in 2004. By process of elimination, the CDA team concluded these particles must be grains of silica, which is found in sand and the mineral quartz on Earth. The consistent size of the grains observed by Cassini, the largest of which were 6 to 9 nanometers, was the clue that told the researchers a specific process likely was responsible.
On Earth, the most common way to form silica grains of this size is hydrothermal activity under a specific range of conditions; namely, when slightly alkaline and salty water that is super-saturated with silica undergoes a big drop in temperature.
"We methodically searched for alternate explanations for the nanosilica grains, but every new result pointed to a single, most likely origin," said co-author Frank Postberg, a Cassini CDA team scientist at Heidelberg University in Germany.
Hsu and Postberg worked closely with colleagues at the University of Tokyo who performed the detailed laboratory experiments that validated the hydrothermal activity hypothesis. The Japanese team, led by Yasuhito Sekine, verified the conditions under which silica grains form at the same size Cassini detected. The researchers think these conditions may exist on the seafloor of Enceladus, where hot water from the interior meets the relatively cold water at the ocean bottom.
The extremely small size of the silica particles also suggests they travel upward relatively quickly from their hydrothermal origin to the near-surface sources of the moon's geysers. From seafloor to outer space, a distance of about 30 miles (50 kilometers), the grains spend a few months to a few years in transit, otherwise they would grow much larger.
The authors point out that Cassini's gravity measurements suggest Enceladus' rocky core is quite porous, which would allow water from the ocean to percolate into the interior. This would provide a huge surface area where rock and water could interact.
The second paper, recently published in Geophysical Research Letters, suggests hydrothermal activity as one of two likely sources of methane in the plume of gas and ice particles that erupts from the south polar region of Enceladus. The finding is the result of extensive modeling to address why methane, as previously sampled by Cassini, is curiously abundant in the plume.
The team found that, at the high pressures expected in the moon's ocean, icy materials called clathrates could form that imprison methane molecules within a crystal structure of water ice. Their models indicate that this process is so efficient at depleting the ocean of methane that the researchers still needed an explanation for its abundance in the plume.
In one scenario, hydrothermal processes super-saturate the ocean with methane. This could occur if methane is produced faster than it is converted into clathrates. A second possibility is that methane clathrates from the ocean are dragged along into the erupting plumes and release their methane as they rise, like bubbles forming in a popped bottle of champagne.
The authors agree both scenarios are likely occurring to some degree, but they note that the presence of nanosilica grains, as documented by the other paper, favors the hydrothermal scenario.
"We didn't expect that our study of clathrates in the Enceladus ocean would lead us to the idea that methane is actively being produced by hydrothermal processes," said lead author Alexis Bouquet, a graduate student at the University of Texas at San Antonio. Bouquet worked with co-author Hunter Waite, who leads the Cassini Ion and Neutral Mass Spectrometer (INMS) team at Southwest Research Institute in San Antonio.
Cassini first revealed active geological processes on Enceladus in 2005 with evidence of an icy spray issuing from the moon's south polar region and higher-than-expected temperatures in the icy surface there. With its powerful suite of complementary science instruments, the mission soon revealed a towering plume of water ice and vapor, salts and organic materials that issues from relatively warm fractures on the wrinkled surface. Gravity science results published in 2014 strongly suggested the presence of a 6-mile- (10-kilometer-) deep ocean beneath an ice shell about 19 to 25 miles (30 to 40 kilometers) thick.
The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory in Pasadena, California, manages the mission for the agency's Science Mission Directorate in Washington. The Cassini CDA instrument was provided by the German Aerospace Center. The instrument team, led by Ralf Srama, is based at the University of Stuttgart in Germany. JPL is a division of the California Institute of Technology in Pasadena.

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The above story is based on materials provided by NASA/Jet Propulsion Laboratory. Note: Materials may be edited for content and length.

Journal Reference:

Hsiang-Wen Hsu, Frank Postberg, Yasuhito Sekine, Takazo Shibuya, Sascha Kempf, Mihály Horányi, Antal Juhász, Nicolas Altobelli, Katsuhiko Suzuki, Yuka Masaki, Tatsu Kuwatani, Shogo Tachibana, Sin-iti Sirono, Georg Moragas-Klostermeyer, Ralf Srama. Ongoing hydrothermal activities within Enceladus. Nature, 2015; 519 (7542): 207 DOI: 10.1038/nature14262