Solar-Powered Battery Woven Into Fabric Overcomes Hurdle for 'Wearable Electronics'

Taek-Soo Kim, Jung-Yong Lee, Jang Wook Choi and colleagues explain that electronic textiles have the potential to integrate smartphone functions into clothes, eyeglasses, watches and materials worn on the skin. Possibilities range from the practical -- for example, allowing athletes to monitor vital signs -- to the aesthetic, such as lighting up patterns on clothing. The bottleneck slowing progress toward development of a wider range of flexible e-fabrics and materials is the battery technology required to power them. Current wearable electronics, such as smartwatches and Google Glass, still require a charger with a cord, and already-developed textile batteries are costly and impractical. To unlink smart technology from the wall socket, the team had to rethink what materials are best suited for use in a flexible, rechargeable battery that's also inexpensive.

They tested unconventional materials and found that they could coat polyester yarn with nickel and then carbon, and use polyurethane as a binder and separator to produce a flexible battery that kept working, even after being folded and unfolded many times. They also integrated lightweight solar cells to recharge the battery without disassembling it from clothing or requiring the wearer to plug in.

The authors acknowledge funding from the National Research Foundation of Korea.

Scientists build world’s smallest FM radio transmitter

US researchers have used graphene to create the world’s smallest FM radio transmitter — a nano-mechanical system that can create FM signals.

A team of researchers from Columbia University, led by mechanical engineering Professor James Hone and electrical engineering Professor Kenneth Shepard, took advantage of graphene’s special properties — its mechanical strength and electrical conduction — and developed a nano-mechanical system that can create FM signals.

“This work is significant in that it demonstrates an application of graphene that cannot be achieved using conventional materials,” Prof. Hone said.

“And it’s an important first step in advancing wireless signal processing and designing ultrathin, efficient cell phones. Our devices are much smaller than any other sources of radio signals, and can be put on the same chip that’s used for data processing,” Prof. Hone added.

In the new study, the team took advantage of graphene’s mechanical ‘stretchability’ to tune the output frequency of their custom oscillator, creating a nano-mechanical version of an electronic component known as a voltage controlled oscillator (VCO).

With a VCO, explained Prof. Hone, it is easy to generate FM signal, exactly what is used for FM radio broadcasting.

The team built a graphene NEMS whose frequency was about 100 megahertz, which lies right in the middle of the FM radio band (87.7 to 108 MHz).

They used low-frequency musical signals (both pure tones and songs from a smartphone) to modulate the 100 MHz carrier signal from the graphene, and then retrieved the musical signals again using an ordinary FM radio receiver.

“This device is by far the smallest system that can create such FM signals,” said Prof. Hone.

The study is published in the journal Nature Nanotechnology.

Scientists Invent Self-Healing Battery Electrode

They reported the advance in the Nov. 19 issue of Nature Chemistry.

"Self-healing is very important for the survival and long lifetimes of animals and plants," said Chao Wang, a postdoctoral researcher at Stanford and one of two principal authors of the paper. "We want to incorporate this feature into lithium ion batteries so they will have a long lifetime as well."

Chao developed the self-healing polymer in the lab of Stanford Professor Zhenan Bao, whose group has been working on flexible electronic skin for use in robots, sensors, prosthetic limbs and other applications. For the battery project he added tiny nanoparticles of carbon to the polymer so it would conduct electricity.

"We found that silicon electrodes lasted 10 times longer when coated with the self-healing polymer, which repaired any cracks within just a few hours," Bao said.

"Their capacity for storing energy is in the practical range now, but we would certainly like to push that," said Yi Cui, an associate professor at SLAC and Stanford who led the research with Bao. The electrodes worked for about 100 charge-discharge cycles without significantly losing their energy storage capacity. "That's still quite a way from the goal of about 500 cycles for cell phones and 3,000 cycles for an electric vehicle," Cui said, "but the promise is there, and from all our data it looks like it's working."

Researchers worldwide are racing to find ways to store more energy in the negative electrodes of lithium ion batteries to achieve higher performance while reducing weight. One of the most promising electrode materials is silicon; it has a high capacity for soaking up lithium ions from the battery fluid during charging and then releasing them when the battery is put to work.

But this high capacity comes at a price: Silicon electrodes swell to three times normal size and shrink back down again each time the battery charges and discharges, and the brittle material soon cracks and falls apart, degrading battery performance. This is a problem for all electrodes in high-capacity batteries, said Hui Wu, a former Stanford postdoc who is now a faculty member at Tsinghua University in Beijing, the other principal author of the paper.

To make the self-healing coating, scientists deliberately weakened some of the chemical bonds within polymers -- long, chain-like molecules with many identical units. The resulting material breaks easily, but the broken ends are chemically drawn to each other and quickly link up again, mimicking the process that allows biological molecules such as DNA to assemble, rearrange and break down.

Researchers in Cui's lab and elsewhere have tested a number of ways to keep silicon electrodes intact and improve their performance. Some are being explored for commercial uses, but many involve exotic materials and fabrication techniques that are challenging to scale up for production.

The self-healing electrode, which is made from silicon microparticles that are widely used in the semiconductor and solar cell industry, is the first solution that seems to offer a practical road forward, Cui said. The researchers said they think this approach could work for other electrode materials as well, and they will continue to refine the technique to improve the silicon electrode's performance and longevity.

Large Graphene Crystals With Exceptional Electrical Properties Created

The team used surface oxygen to grow centimeter-size single graphene crystals on copper. The crystals were about 10,000 times as large as the largest crystals from only four years ago. Very large single crystals have exceptional electrical properties.

"The game we play is that we want nucleation (the growth of tiny 'crystal seeds') to occur, but we also want to harness and control how many of these tiny nuclei there are, and which will grow larger," said Rodney S. Ruoff, professor in the Cockrell School of Engineering. "Oxygen at the right surface concentration means only a few nuclei grow, and winners can grow into very large crystals."

The team -- led by postdoctoral fellow Yufeng Hao and Ruoff of the Department of Mechanical Engineering and the Materials Science and Engineering Program, along with Luigi Colombo, a material scientist with Texas Instruments -- worked for three years on the graphene growth method. The team's paper, "The Role of Surface Oxygen in the Growth of Large Single-Crystal Graphene on Copper," is featured on the cover of the Nov. 8, 2013, issue of Science.

One of the world's strongest materials, graphene is flexible and has high electrical and thermal conductivity that makes it a promising material for flexible electronics, solar cells, batteries and high-speed transistors. The team's understanding of how graphene growth is influenced by differing amounts of surface oxygen is a major step toward improved high-quality graphene films at industrial scale.

The team's method "is a fundamental breakthrough, which will lead to growth of high-quality and large area graphene film," said Sanjay Banerjee, who heads the Cockrell School's South West Academy of Nanoelectronics (SWAN). "By increasing the single-crystal domain sizes, the electronic transport properties will be dramatically improved and lead to new applications in flexible electronics."

Graphene has always been grown in a polycrystalline form, that is, it is composed of many crystals that are joined together with irregular chemical bonding at the boundaries between crystals ("grain boundaries"), something like a patch-work quilt. Large single-crystal graphene is of great interest because the grain boundaries in polycrystalline material have defects, and eliminating such defects makes for a better material.

By controlling the concentration of surface oxygen, the researchers could increase the crystal size from a millimeter to a centimeter. Rather than hexagon-shaped and smaller crystals, the addition of the right amount of surface oxygen produced much larger single crystals with multibranched edges, similar to a snowflake.

"In the long run it might be possible to achieve meter-length single crystals," Ruoff said. "This has been possible with other materials, such as silicon and quartz. Even a centimeter crystal size -- if the grain boundaries are not too defective -- is extremely significant."

"We can start to think of this material's potential use in airplanes and in other structural applications -- if it proves to be exceptionally strong at length scales like parts of an airplane wing, and so on," he said.

Another major finding by the team was that the "carrier mobility" of electrons (how fast the electrons move) in graphene films grown in the presence of surface oxygen is exceptionally high. This is important because the speed at which the charge carriers move is important for many electronic devices -- the higher the speed, the faster the device can perform.

Yufeng Hao says he thinks the knowledge gained in this study could prove useful to industry.

"The high quality of the graphene grown by our method will likely be developed further by industry, and that will eventually allow devices to be faster and more efficient," Hao said.

Single-crystal films can also be used for the evaluation and development of new types of devices that call for a larger scale than could be achieved before, added Colombo.

"At this time, there are no other reported techniques that can provide high quality transferrable films," Colombo said. "The material we were able to grow will be much more uniform in its properties than a polycrystalline film."

Wireless Device Converts 'Lost' Energy Into Electric Power: Metamaterial Cells Provide Electric Power as Efficiently as Solar Panels

The device wirelessly converts the microwave signal to direct current voltage capable of recharging a cell phone battery or other small electronic device, according to a report appearing in the journal Applied Physics Letters in December 2013.

It operates on a similar principle to solar panels, which convert light energy into electrical current. But this versatile energy harvester could be tuned to harvest the signal from other energy sources, including satellite signals, sound signals or Wi-Fi signals, the researchers say.

The key to the power harvester lies in its application of metamaterials, engineered structures that can capture various forms of wave energy and tune them for useful applications.

Undergraduate engineering student Allen Hawkes, working with graduate student Alexander Katko and lead investigator Steven Cummer, professor of electrical and computer engineering, designed an electrical circuit capable of harvesting microwaves.

They used a series of five fiberglass and copper energy conductors wired together on a circuit board to convert microwaves into 7.3V of electrical energy. By comparison, Universal Serial Bus (USB) chargers for small electronic devices provide about 5V of power.

"We were aiming for the highest energy efficiency we could achieve," said Hawkes. "We had been getting energy efficiency around 6 to 10 percent, but with this design we were able to dramatically improve energy conversion to 37 percent, which is comparable to what is achieved in solar cells."

"It's possible to use this design for a lot of different frequencies and types of energy, including vibration and sound energy harvesting," Katko said. "Until now, a lot of work with metamaterials has been theoretical. We are showing that with a little work, these materials can be useful for consumer applications."

For instance, a metamaterial coating could be applied to the ceiling of a room to redirect and recover a Wi-Fi signal that would otherwise be lost, Katko said. Another application could be to improve the energy efficiency of appliances by wirelessly recovering power that is now lost during use.

"The properties of metamaterials allow for design flexibility not possible with ordinary devices like antennas," said Katko. "When traditional antennas are close to each other in space they talk to each other and interfere with each other's operation. The design process used to create our metamaterial array takes these effects into account, allowing the cells to work together."

With additional modifications, the researchers said the power-harvesting metamaterial could potentially be built into a cell phone, allowing the phone to recharge wirelessly while not in use. This feature could, in principle, allow people living in locations without ready access to a conventional power outlet to harvest energy from a nearby cell phone tower instead.

"Our work demonstrates a simple and inexpensive approach to electromagnetic power harvesting," said Cummer. "The beauty of the design is that the basic building blocks are self-contained and additive. One can simply assemble more blocks to increase the scavenged power."

For example, a series of power-harvesting blocks could be assembled to capture the signal from a known set of satellites passing overhead, the researchers explained. The small amount of energy generated from these signals might power a sensor network in a remote location such as a mountaintop or desert, allowing data collection for a long-term study that takes infrequent measurements.

Diamond Imperfections Pave the Way to Technology Gold

Using two-dimensional electronic spectroscopy on pico- and femto-second time-scales, a research team led by Graham Fleming, Vice Chancellor for Research at UC Berkeley and faculty scientist with Berkeley Lab's Physical Biosciences Division, has recorded unprecedented observations of energy moving through the atom-sized diamond impurities known as nitrogen-vacancy (NV) centers. An NV center is created when two adjacent carbon atoms in a diamond crystal are replaced by a nitrogen atom and an empty gap.

"Our use of 2D electronic spectroscopy allowed us to essentially map the flow of energy through the NV center in real time and observe critical quantum mechanical effects," Fleming says. "The results hold broad implications for magnetometry, quantum information, nanophotonics, sensing and ultrafast spectroscopy."

Fleming is the corresponding author of a paper in Nature Physics that describes this research entitled "Vibrational and electronic dynamics of nitrogen-vacancy centres in diamond revealed by two-dimensional ultrafast spectroscopy." The lead author is Vanessa Huxter, former member of Fleming's research group and now a professor at the University of Arizona. Other co-authors are Thomas Oliver and Dmitry Budker, both of whom holds joint appointments with Berkeley Lab and UC Berkeley.

These 2D electronic spectroscopy measurements have provided us with the first window into the ultrafast dynamics of NV centers in diamond," says Huxter. "We were able to observe previously hidden vibrational and electronic properties of the NV center system, including the discovery of vibrational coherences lasting about two picoseconds, which on a quantum mechanical scale is a surprisingly long time."

Given the ubiquitous presence of weak magnetic fields, a sufficiently sensitive detector could be used in a wide range of applications including medical diagnostic and treatment procedures, chemical analyses, energy exploration and homeland security (to detect explosives). Diamond NV centers are held to be one of the finest magnetic sensors possible on the nanoscale. Diamond NV centers are also highly promising candidates for the creation of qubits -- data encoded through quantum-spin rather than electrical charge that will be the heart and soul of quantum computing. Qubits can store exponentially more data and process it billions of times faster than classical computer bits. However, for these rich promises to be fully met, a much better fundamental understanding is needed of the electronic-state dynamics when an NV center is energized.

Says co-author Budker, a UC Berkeley physics professor with Berkeley Lab's Nuclear Sciences Division and leading authority on NV center physics, "NV centers in diamond are already becoming a workhorse in magnetometry and other sensor fields, but they remain somewhat of a black box in that we still don't know understand some important features of their energy levels and dynamics. Our findings in this study provide a starting point for new insights into such critical electronic-state phenomena as dephasing, spin addressing and relaxation."

This study was made possible by the unique 2D electronic spectroscopy technique, which was first developed by Fleming and his research group to study the quantum mechanical underpinnings of photosynthesis. This ultrafast technique enables researchers to track the transfer of energy between atoms or molecules that are coupled (connected) through their electronic and vibrational states. Tracking is done through both time and space. It is accomplished by sequentially flashing light from three laser beams on a sample while a fourth beam serves as a local oscillator to amplify and phase-match the resulting spectroscopic signals.

"By providing femtosecond temporal resolution and nanometer spatial resolution, 2D electronic spectroscopy allows us to simultaneously follow the dynamics of multiple electronic states," says Fleming, who has compared this technology to the early super-heterodyne radios.

In this new study, the use of 2D electronic spectroscopy revealed that the vibrational modes of NV centers in diamond -- a subject of keen scientific interest because these modes directly affect optical and material properties -- are strongly coupled to the defect.

"We were able to identify a number of individual vibrational modes and found that these modes were almost all local to the defect centers and that they were coherent -- quantum mechanically coupled -- for about two picoseconds," says Huxter.

"Through a combination of theory and observation, researchers had suspected that NV center vibrational modes were primarily local to the defect, but our direct observation of the vibrations and their coupling to the excitation states confirms this idea."

In addition, the researchers also were able to measure non-radiative relaxation in the excited state, a property that must be understood and exploited for the creation of qubits.

"We found that the non-radiative relaxation timescale for NV centers in diamond was around four picoseconds, which was slower than we had expected given the number of vibrational states," Huxter says.

The information acquired from this study should make it possible to tune the properties of NV centers in diamonds and open up new avenues for research.

"For example, by optically pumping the NV centers we could specifically excite phonon modes based on their coupling factors," Fleming says. "This would allow the development of diamonds with NV centers that can be used for quantum storage and information processing based on both phonons and spin."

This research was supported primarily by a grant from the National Science Foundation.

Synaptic Transistor Learns While It Computes

Our brains have upwards of 86 billion neurons, connected by synapses that not only complete myriad logic circuits; they continuously adapt to stimuli, strengthening some connections while weakening others. We call that process learning, and it enables the kind of rapid, highly efficient computational processes that put Siri and Blue Gene to shame.

Materials scientists at the Harvard School of Engineering and Applied Sciences (SEAS) have now created a new type of transistor that mimics the behavior of a synapse. The novel device simultaneously modulates the flow of information in a circuit and physically adapts to changing signals.

Exploiting unusual properties in modern materials, the synaptic transistor could mark the beginning of a new kind of artificial intelligence: one embedded not in smart algorithms but in the very architecture of a computer. The findings appear in Nature Communications.

"There's extraordinary interest in building energy-efficient electronics these days," says principal investigator Shriram Ramanathan, associate professor of materials science at Harvard SEAS. "Historically, people have been focused on speed, but with speed comes the penalty of power dissipation. With electronics becoming more and more powerful and ubiquitous, you could have a huge impact by cutting down the amount of energy they consume."

The human mind, for all its phenomenal computing power, runs on roughly 20 Watts of energy (less than a household light bulb), so it offers a natural model for engineers.

"The transistor we've demonstrated is really an analog to the synapse in our brains," says co-lead author Jian Shi, a postdoctoral fellow at SEAS. "Each time a neuron initiates an action and another neuron reacts, the synapse between them increases the strength of its connection. And the faster the neurons spike each time, the stronger the synaptic connection. Essentially, it memorizes the action between the neurons."

In principle, a system integrating millions of tiny synaptic transistors and neuron terminals could take parallel computing into a new era of ultra-efficient high performance.

While calcium ions and receptors effect a change in a biological synapse, the artificial version achieves the same plasticity with oxygen ions. When a voltage is applied, these ions slip in and out of the crystal lattice of a very thin (80-nanometer) film of samarium nickelate, which acts as the synapse channel between two platinum "axon" and "dendrite" terminals. The varying concentration of ions in the nickelate raises or lowers its conductance -- that is, its ability to carry information on an electrical current -- and, just as in a natural synapse, the strength of the connection depends on the time delay in the electrical signal.

Structurally, the device consists of the nickelate semiconductor sandwiched between two platinum electrodes and adjacent to a small pocket of ionic liquid. An external circuit multiplexer converts the time delay into a magnitude of voltage which it applies to the ionic liquid, creating an electric field that either drives ions into the nickelate or removes them. The entire device, just a few hundred microns long, is embedded in a silicon chip.

The synaptic transistor offers several immediate advantages over traditional silicon transistors. For a start, it is not restricted to the binary system of ones and zeros.

"This system changes its conductance in an analog way, continuously, as the composition of the material changes," explains Shi. "It would be rather challenging to use CMOS, the traditional circuit technology, to imitate a synapse, because real biological synapses have a practically unlimited number of possible states -- not just 'on' or 'off.'"

The synaptic transistor offers another advantage: non-volatile memory, which means even when power is interrupted, the device remembers its state.

Additionally, the new transistor is inherently energy efficient. The nickelate belongs to an unusual class of materials, called correlated electron systems, that can undergo an insulator-metal transition. At a certain temperature -- or, in this case, when exposed to an external field -- the conductance of the material suddenly changes.

"We exploit the extreme sensitivity of this material," says Ramanathan. "A very small excitation allows you to get a large signal, so the input energy required to drive this switching is potentially very small. That could translate into a large boost for energy efficiency."

The nickelate system is also well positioned for seamless integration into existing silicon-based systems.

"In this paper, we demonstrate high-temperature operation, but the beauty of this type of a device is that the 'learning' behavior is more or less temperature insensitive, and that's a big advantage," says Ramanathan. "We can operate this anywhere from about room temperature up to at least 160 degrees Celsius."

For now, the limitations relate to the challenges of synthesizing a relatively unexplored material system, and to the size of the device, which affects its speed.

"In our proof-of-concept device, the time constant is really set by our experimental geometry," says Ramanathan. "In other words, to really make a super-fast device, all you'd have to do is confine the liquid and position the gate electrode closer to it."

In fact, Ramanathan and his research team are already planning, with microfluidics experts at SEAS, to investigate the possibilities and limits for this "ultimate fluidic transistor."

He also has a seed grant from the National Academy of Sciences to explore the integration of synaptic transistors into bioinspired circuits, with L. Mahadevan, Lola England de Valpine Professor of Applied Mathematics, professor of organismic and evolutionary biology, and professor of physics.

"In the SEAS setting it's very exciting; we're able to collaborate easily with people from very diverse interests," Ramanathan says.

For the materials scientist, as much curiosity derives from exploring the capabilities of correlated oxides (like the nickelate used in this study) as from the possible applications.

"You have to build new instrumentation to be able to synthesize these new materials, but once you're able to do that, you really have a completely new material system whose properties are virtually unexplored," Ramanathan says. "It's very exciting to have such materials to work with, where very little is known about them and you have an opportunity to build knowledge from scratch."

"This kind of proof-of-concept demonstration carries that work into the 'applied' world," he adds, "where you can really translate these exotic electronic properties into compelling, state-of-the-art devices."

This research was supported by the National Science Foundation (NSF), the Army Research Office's Multidisciplinary University Research Initiative, and the Air Force Office of Scientific Research. The team also benefited from the facilities at the Harvard Center for Nanoscale Systems, a member of the NSF-supported National Nanotechnology Infrastructure Network. Sieu D. Ha, a postdoctoral fellow at SEAS, was the co-lead author; additional coauthors included graduate student You Zhou and Frank Schoofs, a former postdoctoral fellow.

Super-Thin Membranes Clear the Way for Chip-Sized Pumps

But a super-thin silicon membrane developed at the University of Rochester could now make it possible to drastically shrink the power source, paving the way for diagnostic devices the size of a credit card.

"Up until now, electroosmotic pumps have had to operate at a very high voltage -- about 10 kilovolts," said James McGrath, associate professor of biomedical engineering. "Our device works in the range of one-quarter of a volt, which means it can be integrated into devices and powered with small batteries."

McGrath's research paper is being published this week by the journal Proceedings of the National Academy of Sciences.

McGrath and his team use porous nanocrystalline silicon (pnc-Si) membranes that are microscopically thin -- it takes more than one thousand stacked on top of each other to equal the width of a human hair. And that's what allows for a low-voltage system.

A porous membrane needs to be placed between two electrodes in order to create what's known as electroosmotic flow, which occurs when an electric field interacts with ions on a charged surface, causing fluids to move through channels. The membranes previously used in EOPs have resulted in a significant voltage drop between the electrodes, forcing engineers to begin with bulky, high-voltage power sources. The thin pnc Si membranes allow the electrodes to be placed much closer to each other, creating a much stronger electric field with a much smaller drop in voltage. As a result, a smaller power source is needed.

"Up until now, not everything associated with miniature pumps was miniaturized," said McGrath. "Our device opens the door for a tremendous number of applications."

Along with medical applications, it's been suggested that EOPs could be used to cool electronic devices. As electronic devices get smaller, components are packed more tightly, making it easier for the devices to overheat. With miniature power supplies, it may be possible to use EOPs to help cool laptops and other portable electronic devices.

McGrath said there's one other benefit to the silicon membranes. "Due to scalable fabrication methods, the nanocrystalline silicon membranes are inexpensive to make and can be easily integrated on silicon or silica-based microfluid chips."

Persuading Light to Mix It Up With Matter

A sample of bismuth selenide, a topological insulator, is seen inside the test apparatus in Nuh Gedik's lab, ready to be studied using the team's femtosecond laser system and electron spectrometer.

The researchers suggest that this finding could lead to the creation of materials whose electronic properties could be "tuned" in real time simply by shining precise laser beams at them. The work "opens up a new avenue for optical manipulation of quantum states of matter," says Nuh Gedik, the Lawrence C. (1944) and Sarah W. Biedenharn Associate Professor of Physics and senior author of a paper published this week in Science.

Gedik, postdoc Yihua Wang (now at Stanford University), and two other MIT researchers carried out the experiments using a technique Gedik's lab has been developing for several years. Their method involves shooting femtosecond (millionths of a billionth of a second) pulses of mid-infrared light at a sample of material and observing the results with an electron spectrometer, a specialized high-speed camera the team developed.

They demonstrated the existence of a quantum-mechanical mixture of electrons and photons, known as a Floquet-Bloch state, in a crystalline solid. As first theorized by Swiss physicist Felix Bloch, electrons move in a crystal in a regular, repeating pattern dictated by the periodic structure of the crystal lattice. Photons are electromagnetic waves that have a distinct, regular frequency; their interaction with matter leads to Floquet states, named after the French mathematician Gaston Floquet. "Entangling" electrons with photons in a coherent manner generates the Floquet-Bloch state, which is periodic both in time and space.

Victor Galitski, an associate professor of physics at the University of Maryland who was not involved in this research, says, "The importance of this work is difficult to overestimate." He says it "opens new avenues not only for optical control of topological states, but also more generally for engineering of new kinds of electronic states in solid-state systems."

The researchers mixed the photons from an intense laser pulse with the exotic surface electrons on a topological insulator. Their high-speed camera captured snapshots of the exotic state, from its generation to its rapid disappearance, a process lasting only a few hundred femtoseconds. They also found there were different kinds of mixed states when the polarization of the photons changed.

Their findings suggest that it's possible to alter the electronic properties of a material -- for example, changing it from a conductor to a semiconductor -- just by changing the laser beam's polarization. Normally, to produce such dramatic changes in a material's properties, "you have to do something violent to it," Gedik says. "But in this case, it may be possible to do this just by shining light on it. That actually modifies how electrons move in this system. And when we do this, the light does not even get absorbed."

In other situations, light can modify a material's behavior -- but only when it's absorbed, transferring its energy to the material. In this experiment, Gedik says, the light's energy is below the absorption threshold. This is exciting, he says, because it opens up the possibility of switching a material's behavior back and forth without inducing other effects, such as heating -- which would happen if the light were absorbed.

It will take some time to assess possible applications, Gedik says. But, he suggests, this could be a way of engineering materials for specific functions. "Suppose you want a material to do something -- to conduct electricity, or to be transparent, for example. We usually do this by chemical means. With this new method, it may be possible to do this by simply shining light on the materials."

For example, a property called a bandgap -- a crucial characteristic for materials used in computer chips and solar cells -- can be altered by shining a polarized laser beam at the material, Wang says. "You can directly change it, open the bandgap, just with light. It means you can change it from a metal to a semiconductor, for example," he says.

Gedik says that while this experiment was done using bismuth selenide crystals, a basic topological insulator, "what we have done is not specific to topological insulators. It should also be realizable in other materials as well, such as graphene."

"In solid-state physics, we often have no other choice but to rely on serendipity when looking for interesting materials," Galitski says. The new MIT findings "partially challenge this fundamental paradigm by experimentally demonstrating that one can control at will the band structure of a material by subjecting it to an intense optical pulse."

In addition to Gedik and Wang, the team included Pablo Jarillo-Herrero, the Mitsui Career Development Associate Professor in Contemporary Technology, and visiting scientist Hadar Steinberg, both of MIT's physics department. The work was supported by the U.S. Department of Energy and the Army Research Office, and made use of shared facilities at the MIT Center for Materials Science.

The Best Cut for Machining

A new and verified computer model improves the machining of nanoscale semiconductor parts for the electronics industry

Brittle materials such as silicon and ceramics are used extensively in the semiconductor industry to make component parts. Materials cut to have a mirror-like surface yield the best performance, but the precision required is difficult to achieve at such a tiny scale.

Xinquan Zhang at A*STAR's Singapore Institute of Manufacturing Technology, along with co-workers at the same institute and the National University of Singapore, has developed a computer model that allows engineers to predict the best way of cutting different materials using vibration-assisted machining (VAM)1. This technique periodically interrupts the cutting process via the application of small-amplitude and high-frequency displacement to the cutting tool.

"Many researchers have observed that using VAM instead of conventional cutting techniques allows them to make cleaner, fracture-free cuts to most brittle materials," explains Zhang. "Because no theory or model exists to explain or predict this phenomenon, we decided to investigate."

At the nanoscale, brittle materials exhibit a certain degree of plasticity. Each material has a particular depth of cut that allows clean shearing to occur without chipping or fracturing on, or beneath, its surface. This point, known as the critical undeformed chip thickness, is directly correlated with material properties and machining conditions.

Zhang and his team studied the behavior of different brittle materials cut with VAM, during which two modes of cutting occur. In the ductile mode, plastic deformation caused by cutting is followed by elastic rebound and recovery of the material structure between vibrations. The brittle mode, on the other hand, removes material by uncontrolled crack propagation. Making a clean cut during ductile mode -- before the brittle mode dominates -- is therefore desirable.

The researchers modeled the energy consumption of each mode in terms of material removal as the vibrating tool moved, taking into account tool geometry, material properties and the cutting speed.

"By examining energy consumption and material deformation we were able to describe the mechanics when VAM moved from the ductile to the brittle mode," explains Zhang. "We then established a model to predict [the] critical undeformed chip thicknesses by finding the transition point between the two modes."

By examining energy consumption and material deformation we were able to describe the mechanics when VAM moved from the ductile to the brittle mode," explains Zhang. "We then established a model to predict [the] critical undeformed chip thicknesses by finding the transition point between the two modes."

Through a series of experiments, the team verified that the model accurately predicts the critical undeformed chip thicknesses of single-crystal silicon when cut at various VAM speeds.

"Our model will help engineers to select optimized machining parameters depending on their desired material," says Zhang. "Advantages could include higher productivity, lower costs, and improved product quality for semiconductor parts and other nanoscale technologies."

The A*STAR-affiliated researchers contributing to this research are from the Singapore Institute of Manufacturing Technology

People Tend to Communicate With Similar People, Even More Than Previously Thought

The results were obtained by means of a computational method developed by the research group and then applied to massive amounts of anonymised mobile phone call data. The data came from a mobile phone operator's billing system and includes detailed information about the timing of hundreds of millions of mobile phone calls and the age, gender and billing types of anonymised callers and recipients.

The research is linked to computational social science, an area of multidisciplinary research that has become highly important in recent years. In this area, computational methods are used to mine information about human behavior from massive data sets. Rather than focusing on the individual, computational social science strives to understand general properties in the behavior of large groups of people. This contrasts with data collection and mining used for intelligence purposes, which has recently attracted a lot of publicity. Furthermore, the data used is always anonymised.

The research group's computational method is based on statistical analysis of the precise timing of phone calls. This allowed researchers to show that various patterns where phone calls immediately follow each other (for example, A calls B, who then calls C) are more common between people who are similar in terms of age, gender and mutual friends than could be observed based only on numbers of calls made.

Application of the developed method is not only limited to research on communication between people; it also has potential uses in areas like brain research.

Improving the efficiency of solar panels

Light scattering was promoted in the visible part of sunlight's spectrum

At the heart of the blooming solar power industry is the semiconductor material, like silicon or gallium arsenide, which absorbs sunlight and forms the basis of solar panels. It converts electromagnetic energy in the form of sunlight to electrical energy. Now, researchers from London have demonstrated a technique to increase the amount of electrical current produced by a solar panel simply by augmenting its light-facing surface with aluminium nanostructures.

When photons, particles of light, are absorbed by the semiconductor, they knock out electrons, which are passed through a circuit and then to a battery for storage as electricity. However, scientists now want to find ways of increasing the absorption of light in thin layers of semiconductors, so that solar panels can be made using less raw-material and at a lower cost.

Recent research from the Imperial College, London (ICL), has demonstrated one way to increase the electrical current produced by devices in the lab by 22 per cent. By studding the light-receiving surface of gallium-arsenide (Ga-As) devices with aluminium nanocylinders, like the ridges on Lego blocks, the researchers were able to promote the scattering of light in the visible part of the spectrum, which dominates the energy in sunlight.

The scattered light then travels a longer path inside the semiconductor, meaning that more photons can be absorbed and converted into current. It is important that the metal nanocylinders do not absorb the light themselves, as that would prevent it from reaching the panel.

“The advantage of aluminium structures is that their absorption occurs in the ultraviolet part of the spectrum. That means that the absorption losses are limited to the ultraviolet and scattering from the aluminium particle dominates in both the visible and near infrared,” said Dr. Nicholas Hylton, a Research Associate at the Blackett Laboratory, ICL, in an email. Dr. Hylton was lead author of the research group’s paper, published in Scientific Reports on October 18.

This isn’t the first time such nanostructures have been deployed to enhance the performance of solar panels. Earlier, silver and gold nanoparticles have been used because they improved the performance of the devices in the near-infrared part of the electromagnetic spectrum.

“We were able to demonstrate that gold and silver scatter light in the near infrared part of the spectrum but absorb visible light strongly,” Dr. Hylton wrote.

The significance of Dr.Hylton’s work lies in demonstrating aluminium’s better performance over silver and gold nanostructures. For one, aluminium is more abundant and less costly than silver and gold. For another, the 22 per cent spike that aluminium provides, as their paper notes, makes thinner-film solar panels technically feasible without “compromising power conversion efficiencies, thus reducing material consumption.”

Higher efficiency devices could play a significant role in realising energy goals even in India, making them more cost-effective. Already, according to industry trackers, the price of solar power in India has come from Rs. 18/kWh in 2011 to Rs. 7/kWh in 2013, while the price of thermal power is pushing Rs. 4/kWh with subsidies.

Researchers Advance Scheme to Design Seamless Integrated Circuits Etched On Graphene

Bulk materials commonly used to make CMOS transitors and interconnects pose fundamental challenges in continuous shrinking of their feature-sizes and suffer from increasing "contact resistance" between them, both of which lead to degrading performance and rising energy consumption. Graphene-based transistors and interconnects are a promising nanoscale technology that could potentially address issues of traditional silicon-based transistors and metal interconnects.

"In addition to its atomically thin and pristine surfaces, graphene has a tunable band gap, which can be adjusted by lithographic sketching of patterns -- narrow graphene ribbons can be made semiconducting while wider ribbons are metallic. Hence, contiguous graphene ribbons can be envisioned from the same starting material to design both active and passive devices in a seamless fashion and lower interface/contact resistances," explained Kaustav Banerjee, professor of electrical and computer engineering and director of the Nanoelectronics Research Lab at UCSB. Banerjee's research team also includes UCSB researchers Jiahao Kang, Deblina Sarkar and Yasin Khatami. Their work was recently published in the journal Applied Physics Letters.

"Accurate evaluation of electrical transport through the various graphene nanoribbon based devices and interconnects and across their interfaces was key to our successful circuit design and optimization," explained Jiahao Kang, a PhD student in Banerjee's group and a co-author of the study. Banerjee's group pioneered a methodology using the Non-Equilibrium Green's Function (NEGF) technique to evaluate the performance of such complex circuit schemes involving many heterojunctions. This methodology was used in designing an "all-graphene" logic circuit reported in this study.

"This work has demonstrated a solution for the serious contact resistance problem encounterd in conventional semiconductor technology by providing an innovative idea of using an all-graphene device-interconnect scheme. This will significantly simplify the IC fabrication process of graphene based nanoelectronic devices." commented Philip Kim, professor of physics at Columbia University.

As reported in their study, the proposed all-graphene circuits have achieved 1.7X higher noise margins and 1-2 decades lower static power consumption over current CMOS technology. According to Banerjee, with the ongoing worldwide efforts in patterning and doping of graphene, such circuits can be realized in the near future.

"We hope that this work will encourage and inspire other researchers to explore graphene and beyond-graphene emerging 2-dimensional crystals for designing such 'band-gap engineered' circuits in the near future," added Banerjee.

Their research was supported by the National Science Foundation.

Production of Non-Toxic Flame Retardants Simplified

Alarmingly, some 600 people die in household fires in Germany ever year. Often started by nothing more than a small tea light, such fires can soon take hold. Once a few objects are alight, room temperatures shoot up as high as 800 degrees Celsius, and flames quickly spread to other rooms, leaving inhabitants with precious little time to escape after a fire has broken out -- usually no more than around two minutes.

Modern-day apartments and offices contain considerably more combustible materials than they did a few decades ago. Items such as furniture, electronics and electrical equipment are predominantly made up of highly flammable materials that ignite easily, meaning such products would be ablaze in no time at all if it were not for addition of flame retardants. For instance, it only takes eight minutes for a television that has not been fire- proofed to go up in flames, whereas a TV set that has been treated with retardants remains undamaged. Prof. Dr. Manfred Döring and his team at the Fraunhofer Institute for Structural Durability and System Reliability LBF develop flame retardants for polymer materials. These are used inthe transport and construction industries, in electronics and electrical appliances, and many other applications. "Flame retardants prevent fires and slow the spread of the blaze. People are given more time to escape, sometimes up to 20 minutes, which significantly increases the chance of surviving a fire unharmed," says Döring.

Flame retardants must meet high standards

Flame retardants have to satisfy a number of challenging criteria. They must be environmentally friendly, non-hazardous to humans, animals and plants, and must not release any additional toxic fumes when they burn. These additives should not escape the finished product into the atmosphere, or when it comes into contact with water. And researchers must make sure the flame retardant does not react with the plastic or other components in unwelcome ways that might alter the material, influence its functionality or affect its appearance. "Flame resistant work clothing, for instance, has to be machine washable, but cannot lose its protective properties every time it is washed. To prevent the chance of a short circuit developing into a fire, printed circuit boards in electronic devices must remain fully functional and flame retardant over many years, at temperatures that can range from -40 to +60 degrees Celsius," says Döring. He and his team of scientists only work with halogen-free, non-toxic flame retardant additives, and tailor each substance to the particular plastic in question. Depending on the intended application for the material, they use inorganic compounds and compounds containing nitrogen and phosphorus.

One such product will be on display at the K 2013 trade fair from 16 to 23 October in Düsseldorf. Fraunhofer LBF scientists are presenting a halogen-free, polymeric flame retardant for fibers that is suitable for use in flame retardant seat covers, for instance. What is unique about their product is that the scientists introduce the polymeric flame retardant as part of the extrusion process, a technique that is commonly used in the plastics industry. A polymer that is suitable for fiber spinning is mixed with a flame retardant polymer in the extruder. This is the machine that feeds raw plastic material along a jacketed screw that heats, melts and compacts the plastic before passing it through another tool under pressure to form a continuous profile. The flame retardant is evenly mixed into the base polymer by simple mechanical action. This method gives plastics manufacturers the advantage of being able to personally control the amount of flame retardant polymer that gets added, meaning that they are able to produce flame resistant polymers according to their own formulae for the very first time.

The research team at Fraunhofer LBF is in the process of setting up a fire safety laboratory that will offer a broad range of services towards the end of 2014. Chemists and engineers will then conduct efficiency tests on flame retardants found in polymers, and develop formulae for synthetic polymers such as thermoplastics, thermosets and composites. They will examine and test the efficiency of multi-component systems, or what experts refer to as "synergetic mixtures" -- compounds that multiply the inherent properties of their individual components. The scientists can also synthesize halogen-free fire retardants and scale up the synthesis as required. The range of possible applications is vast, given the growing share of components made of plastic, all of which have to be treated with flame retardants.

Topological Light: Living On the Edge

enlarge

Artistic rendering of real data and real SEM image (false colored) from experiment. The lit resonators show light racing around the edge of the silicon chip unimpeded, avoiding defects (here a missing resonator). (Credit: E. Edwards/JQI. Figure attributes (color, lighting) altered for artistic purposes with permission of authors.)

Quantum Hall physics, inherently topological, has been seen in electronic devices and in dilute atomic ensembles. In the two-dimensional electron case, current flows along an edge/interface ("edge states") even in the presence of defects or other physical distortions in the sample -- this arises from global properties of the material. This is strange when contrasted with conventional conductors/insulators, where the transport is impeded due the presence of disorder.

In this week's issue of Nature Photonics scientists at the Joint Quantum Institute report the first observation of such topological effects for light in two dimensions. To accomplish this, they built a structure to guide infrared light over the surface of a room temperature, silicon-on-insulator chip. Amazingly, they directly observed light racing around the boundary, impervious to defects. These photonic "edge states" are directly analogous to the quantum Hall effect for electrons.

Since silicon is the preferred material for most electronics this novel design assists with the miniaturization of optical communication technology, bringing photons a little closer to their electronic circuit counterparts. The work is a realization of a theoretical proposal by this same group of JQI scientists and their collaborators more than a year ago.

Edge States and Ring Resonators

Electrons can occupy topological edge states because they are charged particles whose energy spectrum can be dramatically modified by large magnetic fields. To simplify, a magnetic interaction is key for realizing quantum Hall states. The question here to ask is how researchers can design a material where photons -- massless, charge-free, packets of energy -- flow as if they are being manipulated by a super strong magnet. To put it another way, how can the energy spectrum of light be modified to support robust topological states? And what do these photonic edge states look like?

In the JQI design, the light moves through a 2D landscape consisting of nearly flat ring-shaped silicon waveguides called resonators. By comparison, the arena for electrons is typically at the two-dimensional interface between two sheets of semiconductor. What the JQI scientists showed was that indeed light can, under the right circumstances, circulate around the edge of the silicon chip, without significant loss of energy, and do so even in the presence of defects.

The array of silicon rings is designed to only let the light waves inside-- "resonate"-- if they have the right wavelength (the circumference of the ring equaling an integral number of wavelengths). In other words, if the light frequency matches the resonant conditions of the ring it will enter the waveguide and make many circuits. For an off-resonance condition less light will inhabit the ring. Light with one polarization (the light's electric field pointing up or down) will, furthermore, circulate preferentially in one direction around the ring, clockwise or anti-clockwise. For the enthusiasts, the clockwise and anti-clockwise modes, in combination with the resonator array design, allows the photonic system to be analogous to an electron (spin) interacting with a magnet. The researchers created a photonic system that experiences a so-called synthetic or effective magnetic field [[see this link on the design proposal by this same group and this link on synthetic fields in ultracold atoms]].

This breaking of the symmetry of travel around rings is what can cause the cancelling-out of light propagation through the body of the device but not around the edge. It is also what reduces the amount of light energy wasted when light scatters or moves backwards around the edge or meets with a defect such as a defective resonator ring. Thus the JQI device displays the hallmark of topological behavior: persistent flow in the form of an edge state and near immunity against defects. The scientists went out of their way to deliberately turn off some resonators, thus simulating the industrial conditions of mass production -- a process prone to the presence of faulty components even in the best of fabrication circumstances. They also demonstrated the edge flow in the presence of unpredicted defects in the device.

In all of those resonator-to-resonator transfers, at least a little bit of the light gets lost, and this wasted energy is what the researchers use to image the light paths through the device. When the resonator array is tuned with the right frequency and temperature for general (non-topological) transmission, that's what you get: light moves through the whole of the array. However, when the system is tuned to facilitate edge states, sure enough, no light moves through the body of the array; it only skirts the edge of the array -- in a direct analogy to electron movement in a quantum Hall state. Notably, this scheme is a realization of the quantum spin Hall effect, where photonic (pseudo-)spins take the place of electron charge.

Possible Applications

"By tuning the resonators with temperature, we can make this topological array quite flexible," says Jacob Taylor, one of the JQI researchers. "The array isn't designed for one frequency only." Furthermore, the architecture of the array, which can be expanded to suite the need, fits in with the expectation that components such as this will need to be scaled up for use in future quantum computers, especially those that use photons as parts of hybrid electron-photon-atom systems.

JQI scientist and lead author, Mohammad Hafezi explains why edge states for photons might have an advantage over electron edge states for certain applications: "Photonic systems are remarkably malleable since photons can be easily guided inside the waveguides. Therefore, one can think of making photonic systems with non-trivial topologies, like Mobius strip, tori etc."

What can be done with a photonic array like this? One immediate advantage of edge states is that the arrays can be used for producing delays in photonic chips, where it is desirable to slow down a signal without being sensitive to fabrication errors. Other future uses: as filters and optical switches. Furthermore, by concentrating light in only two dimensions rather than three, the JQI scientists believe they can achieve certain nonlinear quantum effects, which can only occur with intense light.

Gravitational Waves Help Us Understand Black-Hole Weight Gain

A paper in today's issue of Science pits the front-running ideas about the growth of supermassive black holes against observational data -- a limit on the strength of gravitational waves, obtained with CSIRO's Parkes radio telescope in eastern Australia.

"This is the first time we've been able to use information about gravitational waves to study another aspect of the Universe -- the growth of massive black holes," co-author Dr Ramesh Bhat from the Curtin University node of the International Centre for Radio Astronomy Research (ICRAR) said.

"Black holes are almost impossible to observe directly, but armed with this powerful new tool we're in for some exciting times in astronomy. One model for how black holes grow has already been discounted, and now we're going to start looking at the others."

The study was jointly led by Dr Ryan Shannon, a Postdoctoral Fellow with CSIRO, and Mr Vikram Ravi, a PhD student co-supervised by the University of Melbourne and CSIRO.

Einstein predicted gravitational waves -- ripples in space-time, generated by massive bodies changing speed or direction, bodies like pairs of black holes orbiting each other.

When galaxies merge, their central black holes are doomed to meet. They first waltz together then enter a desperate embrace and merge.

"When the black holes get close to meeting they emit gravitational waves at just the frequency that we should be able to detect," Dr Bhat said.

Played out again and again across the Universe, such encounters create a background of gravitational waves, like the noise from a restless crowd.

Astronomers have been searching for gravitational waves with the Parkes radio telescope and a set of 20 small, spinning stars called pulsars.

Pulsars act as extremely precise clocks in space. The arrival time of their pulses on Earth are measured with exquisite precision, to within a tenth of a microsecond.

When the waves roll through an area of space-time, they temporarily swell or shrink the distances between objects in that region, altering the arrival time of the pulses on Earth.

The Parkes Pulsar Timing Array (PPTA), and an earlier collaboration between CSIRO and Swinburne University, together provide nearly 20 years worth of timing data. This isn't long enough to detect gravitational waves outright, but the team say they're now in the right ballpark.

"The PPTA results are showing us how low the background rate of gravitational waves is," said Dr Bhat.

"The strength of the gravitational wave background depends on how often supermassive black holes spiral together and merge, how massive they are, and how far away they are. So if the background is low, that puts a limit on one or more of those factors."

Armed with the PPTA data, the researchers tested four models of black-hole growth. They effectively ruled out black holes gaining mass only through mergers, but the other three models are still a possibility.

Dr Bhat also said the Curtin University-led Murchison Widefield Array (MWA) radio telescope will be used to support the PPTA project in the future.

"The MWA's large view of the sky can be exploited to observe many pulsars at once, adding valuable data to the PPTA project as well as collecting interesting information on pulsars and their properties," Dr Bhat said.

Method of Recording Brain Activity Could Lead to Mind-Reading Devices, Stanford Scientists Say

Using a novel method, the researchers collected the first solid evidence that the pattern of brain activity seen in someone performing a mathematical exercise under experimentally controlled conditions is very similar to that observed when the person engages in quantitative thought in the course of daily life.

"We're now able to eavesdrop on the brain in real life," said Josef Parvizi, MD, PhD, associate professor of neurology and neurological sciences and director of Stanford's Human Intracranial Cognitive Electrophysiology Program. Parvizi is the senior author of the study, published Oct. 15 in Nature Communications. The study's lead authors are postdoctoral scholar Mohammad Dastjerdi, MD, PhD, and graduate student Muge Ozker.

The finding could lead to "mind-reading" applications that, for example, would allow a patient who is rendered mute by a stroke to communicate via passive thinking. Conceivably, it could also lead to more dystopian outcomes: chip implants that spy on or even control people's thoughts.

"This is exciting, and a little scary," said Henry Greely, JD, the Deane F. and Kate Edelman Johnson Professor of Law and steering committee chair of the Stanford Center for Biomedical Ethics, who played no role in the study but is familiar with its contents and described himself as "very impressed" by the findings. "It demonstrates, first, that we can see when someone's dealing with numbers and, second, that we may conceivably someday be able to manipulate the brain to affect how someone deals with numbers."

The researchers monitored electrical activity in a region of the brain called the intraparietal sulcus, known to be important in attention and eye and hand motion. Previous studies have hinted that some nerve-cell clusters in this area are also involved in numerosity, the mathematical equivalent of literacy.

However, the techniques that previous studies have used, such as functional magnetic resonance imaging, are limited in their ability to study brain activity in real-life settings and to pinpoint the precise timing of nerve cells' firing patterns. These studies have focused on testing just one specific function in one specific brain region, and have tried to eliminate or otherwise account for every possible confounding factor. In addition, the experimental subjects would have to lie more or less motionless inside a dark, tubular chamber whose silence would be punctuated by constant, loud, mechanical, banging noises while images flashed on a computer screen.

"This is not real life," said Parvizi. "You're not in your room, having a cup of tea and experiencing life's events spontaneously." A profoundly important question, he said, is: "How does a population of nerve cells that has been shown experimentally to be important in a particular function work in real life?"

His team's method, called intracranial recording, provided exquisite anatomical and temporal precision and allowed the scientists to monitor brain activity when people were immersed in real-life situations. Parvizi and his associates tapped into the brains of three volunteers who were being evaluated for possible surgical treatment of their recurring, drug-resistant epileptic seizures.

The procedure involves temporarily removing a portion of a patient's skull and positioning packets of electrodes against the exposed brain surface. For up to a week, patients remain hooked up to the monitoring apparatus while the electrodes pick up electrical activity within the brain. This monitoring continues uninterrupted for patients' entire hospital stay, capturing their inevitable repeated seizures and enabling neurologists to determine the exact spot in each patient's brain where the seizures are originating.

During this whole time, patients remain tethered to the monitoring apparatus and mostly confined to their beds. But otherwise, except for the typical intrusions of a hospital setting, they are comfortable, free of pain and free to eat, drink, think, talk to friends and family in person or on the phone, or watch videos.

The electrodes implanted in patients' heads are like wiretaps, each eavesdropping on a population of several hundred thousand nerve cells and reporting back to a computer.

In the study, participants' actions were also monitored by video cameras throughout their stay. This allowed the researchers later to correlate patients' voluntary activities in a real-life setting with nerve-cell behavior in the monitored brain region.

As part of the study, volunteers answered true/false questions that popped up on a laptop screen, one after another. Some questions required calculation -- for instance, is it true or false that 2+4=5? -- while others demanded what scientists call episodic memory -- true or false: I had coffee at breakfast this morning. In other instances, patients were simply asked to stare at the crosshairs at the center of an otherwise blank screen to capture the brain's so-called "resting state."

Consistent with other studies, Parvizi's team found that electrical activity in a particular group of nerve cells in the intraparietal sulcus spiked when, and only when, volunteers were performing calculations.

Afterward, Parvizi and his colleagues analyzed each volunteer's daily electrode record, identified many spikes in intraparietal-sulcus activity that occurred outside experimental settings, and turned to the recorded video footage to see exactly what the volunteer had been doing when such spikes occurred.

They found that when a patient mentioned a number -- or even a quantitative reference, such as "some more," "many" or "bigger than the other one" -- there was a spike of electrical activity in the same nerve-cell population of the intraparietal sulcus that was activated when the patient was doing calculations under experimental conditions.

That was an unexpected finding. "We found that this region is activated not only when reading numbers or thinking about them, but also when patients were referring more obliquely to quantities," said Parvizi.

"These nerve cells are not firing chaotically," he said. "They're very specialized, active only when the subject starts thinking about numbers. When the subject is reminiscing, laughing or talking, they're not activated." Thus, it was possible to know, simply by consulting the electronic record of participants' brain activity, whether they were engaged in quantitative thought during nonexperimental conditions.

Any fears of impending mind control are, at a minimum, premature, said Greely. "Practically speaking, it's not the simplest thing in the world to go around implanting electrodes in people's brains. It will not be done tomorrow, or easily, or surreptitiously."

Parvizi agreed. "We're still in early days with this," he said. "If this is a baseball game, we're not even in the first inning. We just got a ticket to enter the stadium."

The study was funded by the National Institutes of Health (grant R01NS0783961), the Stanford NeuroVentures Program, and the Gwen and Gordon Bell Family. Additional co-authors were postdoctoral scholar Brett Foster, PhD, and research assistant Vinitha Rangarajan.

An Optical Switch Based On a Single Nano-Diamond

The scientific results of this study have been published in Nature Physics.

Electronic transistors have become a key component to modern electronics, drastically improving the speed of information processing of current technologies. An electronic transistor is a semiconductor device used to amplify and switch electronic signals. The much sought after optical transistor (the photonic counterpart of the electronic transistor) is poised to become a central ingredient in the development of optical signal processing. The motivation for using photons rather than electrons not only comes from their faster dynamics but also from their weaker interaction with the environment, which enable a high degree of integration and the realization of quantum operations.

Prior studies have demonstrated that single dye molecules can be operated as optical transistors with the disadvantage that they worked exclusively at extremely low temperatures. Such restrictions on the temperature made these optical transistors cumbersome for application to quantum computing.

However in this recent ICFO study, scientists have shown that a nano-size diamond at room temperature can act as an efficient optical switch controllable with light. A Nano-diamond containing a nitrogen impurity behaves like an artificial atom although much more stable at room temperature than a real atom due to its encapsulation. The ICFO scientists discovered a novel physical mechanism that enables the control of the way the nano-diamond interacts with light. While excited to its ON state by a green laser, a suitable near infrared illumination was found to act as an efficient and fast way to switch it OFF. Based on this simple concept, they were able to modulate the optical nano-diamond ON and OFF at extremely high speeds, demonstrating its robustness and viability for very fast information processing and quantum computer operations.

Quidant remarks that "what is really attractive about our discovery is that our nano-switch combines very small dimensions (compatible with integrating a large number of them in a small area) with very fast response time (meaning lots of operations in a short time) and operation at room temperature."

This new technique will contribute to the development of future integrated optical circuits as well as quantum information processing for quantum computing.

This work is a collaborative effort between the research groups at ICFO led by ICREA Professors at ICFO Javier García de Abajo and Romain Quidant.

World Record: Wireless Data Transmission at 100 Gbit/S

In their record experiment, 100 gigabits of data per second were transmitted at a frequency of 237.5 GHz over a distance of 20 m in the laboratory. In previous field experiments under the "Millilink" project funded by the BMBF, rates of 40 gigabits per second and transmission distances of more than 1 km were reached. For their latest world record, the scientists applied a photonic method to generate the radio signals at the transmitter. After radio transmission, fully integrated electronic circuits were used in the receiver.

"Our project focused on integration of a broadband radio relay link into fiber-optical systems," Professor Ingmar Kallfass says. He coordinated the "Millilink" project under a shared professorship funded by the Fraunhofer Institute for Applied Solid State Physics (IAF) and the Karlsruhe Institute of Technology (KIT). Since early 2013, he has been conducting research at Stuttgart University. "For rural areas in particular, this technology represents an inexpensive and flexible alternative to optical fiber networks, whose extension can often not be justified from an economic point of view." Kallfass also sees applications for private homes: "At a data rate of 100 gigabits per second, it would be possible to transmit the contents of a blue-ray disk or of five DVDs between two devices by radio within two seconds only."

In the experiments, latest photonic and electronic technologies were combined: First, the radio signals are generated by means of an optical method. Several bits are combined by so-called data symbols and transmitted at the same time. Upon transmission, the radio signals are received by active integrated electronic circuits.

The transmitter generates the radio signals by means of an ultra-broadband so-called photon mixer made by the Japanese company NTT-NEL. For this, two optical laser signals of different frequencies are superimposed on a photodiode. An electrical signal results, the frequency of which equals the frequency difference of both optical signals, here, 237.5 GHz. The millimeter-wave electrical signal is then radiated via an antenna.

"It is a major advantage of the photonic method that data streams from fiber-optical systems can directly be converted into high-frequency radio signals," Professor Jürg Leuthold says. He proposed the photonic extension that was realized in this project. The former head of the KIT Institute of Photonics and Quantum Electronics (IPQ) is now affiliated with ETH Zurich. "This advantage makes the integration of radio relay links of high bit rates into optical fiber networks easier and more flexible." In contrast to a purely electronic transmitter, no intermediate electronic circuit is needed. "Due to the large bandwidth and the good linearity of the photon mixer, the method is excellently suited for transmission of advanced modulation formats with multiple amplitude and phase states. This will be a necessity in future fiber-optical systems," Leuthold adds.

Reception of radio signals is based on electronic circuits. In the experiment, a semiconductor chip was employed that was produced by the Fraunhofer Institute of Applied Solid State Physics (IAF) within the framework of the "Millilink" project. The semiconductor technology is based on high-electron-mobility transistors (HEMT) enabling the fabrication of active, broadband receivers for the frequency range between 200 and 280 GHz. The integrated circuits have a chip size of a few square millimeters only. The receiver chip can also cope with advanced modulation formats. As a result, the radio link can be integrated into modern optical fiber networks in a bit-transparent way.

Already in May this year the team succeeded in transmitting a data rate of 40 gigabits per second over a long distance in the laboratory using a purely electronic system. In addition, data were transmitted successfully over a distance of one kilometer from one high-riser to another in the Karlsruhe City center. "The long transmission distances in "Millilink" were reached with conventional antennas that may be replaced by fully integrated miniaturized antenna designs in future compact systems for indoor use," says Professor Thomas Zwick, Head of the KIT Institut für Hochfrequenztechnik und Elektronik (Institute of High-Frequency Technology and Electronics). The present data rate can be still increased. "By employing optical and electrical multiplexing techniques, i.e., by simultaneously transmitting multiple data streams, and by using multiple transmitting and receiving antennas, the data rate could be multiplied," says Swen König from the KIT Institute of Photonics and Quantum Electronics (IPQ), who conceived and conducted the recent world-record experiment. "Hence, radio systems having a data rate of 1 terabit per second appear to be feasible."

Superlative Supercapacitors - A Moonshot Idea

Batteries have a bad reputation. They're made of toxic materials and charge very slowly. Richard Kaner talks about his solution in The Super Supercapacitor, a SolveForX talk created as part of the GE Focus Forward series.

In general batteries have high energy storage but take a long time to charge and discharge. A capacitor can charge and discharge quickly but have very low energy storage capabilities. Kaner is expecting his new graphene supercapacitors to store high amounts of energy and charge at least one hundred times faster than a battery.

http://www.kurzweilai.net/graphene-micro-supercapacitors-to-replace-batteries-for-microelectonics-devices

Kaner was researching graphene in his lab. Graphene is a strong flexible carbon-based material but production methods were not efficient. Kaner and his research assistant Maher El-Kady developed a new process using sheets of plastic and curing through dvds and a personal computer disc drive.

Serendipity came when Maher found that graphene could act as a supercapacitor. With a specimen of graphene and two leads he charged a light in a few seconds and kept the light running for five minutes.

The possibilities here are wide open. Immediately charging our electronic devices will bring convenience to most of us, but further down the line energy storage and transmission could be changed to meet future energy needs. Charging an electric vehicle could take minutes, and when exhausted graphene can be recycled back into its carbon components much easier than battery materials.

http://dailybruin.com/2013/02/28/professor-and-graduate-student-develop-battery-like-product/

New technique lets you feel textures on touchscreen:

Smartphone users can now ‘feel’ images and objects seen on their touchscreen!

In a game-changing invention, engineers at Disney Research, Pittsburgh, have developed a new technique that allows you to feel the texture of objects seen on a flat touchscreen.

The novel algorithm enables a person sliding a finger across a topographic map displayed on a touchscreen to feel the bumps and curves of hills and valleys, despite the screen’s smooth surface.

The technique is based on the fact that when a person slides a finger over a real physical bump, he perceives the bump largely because lateral friction forces stretch and compress skin on the sliding finger.

By altering the friction encountered as a person’s fingertip glides across a surface, the Disney algorithm can create a perception of a 3D bump on a touch surface.

The method can be used to simulate the feel of a wide variety of objects and textures.

“Our brain perceives the 3D bump on a surface mostly from information that it receives via skin stretching,” said Ivan Poupyrev, who directs Disney Research, Pittsburgh’s Interaction Group.

“Therefore, if we can artificially stretch skin on a finger as it slides on the touchscreen, the brain will be fooled into thinking an actual physical bump is on a touchscreen even though the touch surface is completely smooth,” Poupyrev said in a statement.

In experiments, researchers used electrovibration to modulate the friction between the sliding finger and the touch surface with electrostatic forces.

Researchers created and validated a psychophysical model that closely simulates friction forces perceived by the human finger when it slides over a real bump.

The model was then incorporated into an algorithm that dynamically modulates the frictional forces on a sliding finger so that they match the tactile properties of the visual content displayed on the touchscreen along the finger’s path.

A broad variety of visual artifacts thus can be dynamically enhanced with tactile feedback that adjusts as the visual display.

“The traditional approach to tactile feedback is to have a library of canned effects that are played back whenever a particular interaction occurs,” said Ali Israr, a Disney Research, Pittsburgh research engineer who was the lead on the project.

“This makes it difficult to create a tactile feedback for dynamic visual content, where the sizes and orientation of features constantly change. With our algorithm we do not have one or two effects, but a set of controls that make it possible to tune tactile effects to a specific visual artifact on the fly,” Israr said.

The new research will be presented at the ACM Symposium on User Interface Software and Technology in St Andrews, Scotland.

Continuous Monitoring Contact Lenses:

Current medical science only gives us body scans at one point in time. Babak Parviz discusses his solution to this problem in his SolveForX talk, Continuous Body Monitoring.

Today’s data collection devices, if not in physical contact with the body, are not sending out information. There are possibilities for implanting but our bodies generally react poorly to foreign objects. Parviz’s targeted interface on the human body is the surface of the eye.

Tears exist with much of the same chemical makeup as blood, so contact lenses are a solution to show what is going on inside a patient’s body without actually going inside the body. Contact lenses are used by more than one hundred million people and have existed for decades, giving users a comfortable method of existing with a continuous sensor.

As a receiver the lens could act as a display for the user, with cell phone towers beaming information to a unit in the user’s pocket. An augmented reality application is the most feasible use for a lens receiver. Long term Babak says that screens exist to bring information to the retina, and many screens could be consolidated into one display per human being.

The semiconductor industry is constantly churning out smaller sensors allowing the lenses to collect and disperse information. Some sensors are down to 50 nanometers, approaching the size of a single cell in the body. Using miniaturization technology along with flexible sensor technology Babak is developing the contact lens sensors.

Lenses are being tested now with miniature glucose sensors, antenna and readout circuits. The system can be powered remotely with RF broadcast to wake up, take the measurement and send the data before powering back down. Very small devices consume very small amounts of power, and the entire system can be run with 3 microWatts.

• 
  

video:http://www.youtube.com/embed/d6g581tJ7bM

Printed Electronics: A Multi-Touch Sensor Customizable With Scissors

Video: http://www.youtube.com/watch?v=wnTG_ZTYdVk

— If a pair of long pants is too long, it is cut to length. A board that does not fit into a bookcase is sawed to the right length. People often customize the size and shape of materials like textiles and wood without turning to specialists like tailors or carpenters. In the future this should be possible with electronics, according to the vision of computer scientists from Saarbrücken. Together with researchers from the MIT Media Lab, they developed a printable multi-touch sensor whose shape and size everybody can alter. A new circuit layout makes it robust against cuts, damage, and removed areas.

Today the researchers are presenting their work at the conference "User Interface and Technology" (UIST) in St. Andrews, Scotland.

"Imagine a kid takes our sensor film and cuts out a flower with stem and leaves. If you touch the blossom with a finger, you hear the buzzing of a bumblebee," Jürgen Steimle says. He reports that programs and apps are easily imaginable to help parents connect touching a sensor film with the suitable sound effect. Steimle, 33, has a doctoral degree in computer science and is doing research at the Max-Planck Institute for Informatics. He also heads the Embodied Interaction research group at the Cluster of Excellence on Multimodal Computing and Interaction.

Simon Olberding is the doctoral candidate and the lead developer of the new sensor. He sees a further application of the new technology in so-called interactive walls used for discussions and brainstorming. "So far, such a wall frays and scuffs quickly as we hammer nails into it, stick notes or posters on it, and damage it while removing them. By customizing and pasting on our new sensor you can make every surface interactive no matter if it is the wristband of a watch, a cloth on a trade fair table, or wallpaper," Olberding says.

As basic technology the scientists use so-called "printed electronics." This term summarizes electrical components and devices which are printed. The approach is similar to that of inkjet printers. Instead of printing with normal ink, electrically-functional electronic ink is printed on flexible, thin films (so-called substrates). "The factory costs are so low that printing our DIN A4 film on our special printer in the lab costs us about one US dollar," Steimle says.

But you need more than printed electronics to make a sensor robust against cuts, damage, and removed areas. So far the circuit layout of a multi-touch sensor has been similar to graph paper. The wires run horizontally, vertically, and parallel to each other. At the intersection of one parallel and one horizontal layer you find the touch-sensitive electrodes. Via the wires they are connected to a controller. This type of layout requires only a minimal number of wires, but is not robust. Since each wire addresses several electrodes, a small cut has a huge effect: many electrodes become unusable and possibly large sensor areas do not work anymore. "It was not easy to find an alternative layout, robust enough for our approach," Olberding says. They took their inspiration from nature, looking at the human nerve system and fungal root networks, and thus came up with two basic layouts. The so-called star topology has the controller in the center. It is connected to every electrode separately. The so-called tree topology also has the controller in its center connected to each electrode separately. But the wires are bundled similarly to a tree structure. They all run through a vertical line in the middle and then branch off to reach their electrodes.

The scientists found out that the star topology supports often-used basic forms like triangles, rectangles, or ovals best. Furthermore, it is suitable for shapes commonly used for crafts, like stars, clouds, or hearts. In contrast, with the tree topology it is possible to cut out whole areas. The researchers were also able to combine both layouts in a space-saving way, so that the sensor supports all basic forms.

"We assume that printed sensors will be so inexpensive that multi-touch sensing capability will become an inherent part of the material. Users can take it to create interactive applications or just to write on it," Steimle explains. This vision is not so far away, as a prediction from the "Organic and Printed Electronic Association" shows. The international industry association forecast that flexible consumer electronics will be available for end-users between the years 2017 and 2020.