National Institute of Standards and Technology

Researchers demonstrate ultrasonically propelled nanorods spin dizzyingly fast.

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Vibrate a solution of rod-shaped metal nanoparticles in water with ultrasound and they’ll spin around their long axes like tiny drill bits. Why? No one yet knows exactly. But researchers at the National Institute of Standards and Technology (NIST) have clocked their speed—and it’s fast. At up to 150,000 revolutions per minute, these nanomotors rotate 10 times faster than any nanoscale object submerged in liquid ever reported.

The discovery of this dizzying rate has opened up the possibility that they could be used not only for moving around inside the body—the impetus for the research—but also for high-speed machining and mixing.

Scientists have been studying how to make nanomotors move around in liquids for the past several years. A group at Penn State looking for a biologically friendly way to propel nanomotors first observed that metal nanorods were moving and rotating in response to ultrasound in 2012. Another group at the University of California San Diego then directed the metal rods’ forward motion using a magnetic field. The Penn State group then demonstrated that these nanomotors could be propelled inside of a cancer cell.

But no one knew why or how fast the nanomotors were spinning. The latter being a measurement problem, researchers at NIST worked with the Penn State group to solve it.

“If nanomotors are to be used in a biological environment, then it is important to understand how they interact with the liquid and objects around them,” says NIST project leader Samuel Stavis. “We used nanoparticles to trace the flow of water around the nanomotors, and we used that measurement to infer their rate of rotation. We found that the nanomotors were spinning surprisingly rapidly.”

The NIST team clocked the nanomotors’ rotation by mixing the 2-micrometer-long, 300-nanometer-wide gold rods with 400-nanometer-diameter polystyrene beads in water and putting them between glass and silicon plates with a speaker-type shaker beneath. They then vibrated the shaker at an ultrasonic tone of 3 megahertz—much too high for you or your dog to hear—and watched the motors and beads move.

As the motors rotate in water, they create a vortex around them. Beads that get close get swept up by the vortex and swirl around the rods. By measuring how far the beads are from the rods and how fast they move, the group was able to work out how quickly the motors were spinning—with an important caveat.

“The size of the nanorods is important in our measurements” says NIST physicist Andrew Balk. “We found that even small variations in the rod’s dimensions cause large measurement uncertainties, so they need to be fabricated as uniformly as possible for future studies and applications.”

According to the researchers, the speed of the nanomotors’ rotation seems to be independent of their forward motion. Being able to control the “speed and feed” of the nanomotors independently would open up the possibility that they could be used as rotary tools for machining and mixing.

Future avenues of research include trying to discover exactly why the motors rotate and how the vortex around the rods affects their interactions with each other.

Read more at: http://phys.org/news/2014-07-ultrasonically-propelled-nanorods-dizzyingly-fast.html#jCp

Future electronics may depend on lasers, not quartz

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Nearly all electronics require devices called oscillators that create precise frequencies—frequencies used to keep time in wristwatches or to transmit reliable signals to radios. For nearly 100 years, these oscillators have relied upon quartz crystals to provide a frequency reference, much like a tuning fork is used as a reference to tune a piano. However, future high-end navigation systems, radar systems, and even possibly tomorrow’s consumer electronics will require references beyond the performance of quartz.

 Future electronics may depend on lasers, not quartz

Now, researchers in the laboratory of Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics at Caltech, have developed a method to stabilize  in the range of gigahertz, or billions of cycles per second—using a pair of laser beams as the reference, in lieu of a crystal.

Quartz crystals “tune” oscillators by vibrating at relatively low frequencies—those that fall at or below the range of megahertz, or millions of cycles per second, like radio waves. However, quartz crystals are so good at tuning these low frequencies that years ago, researchers were able to apply a technique called electrical frequency division that could convert higher-frequency microwave signals into lower-frequency signals, and then stabilize these with quartz.

The new technique, which Vahala and his colleagues have dubbed electro-optical frequency division, builds off of the method of optical frequency division, developed at the National Institute of Standards and Technology more than a decade ago. “Our new method reverses the architecture used in standard crystal-stabilized microwave oscillators—the ‘quartz’ reference is replaced by optical signals much higher in frequency than the microwave signal to be stabilized,” Vahala says.

Jiang Li—a Kavli Nanoscience Institute postdoctoral scholar at Caltech and one of two lead authors on the paper, along with graduate student Xu Yi—likens the method to a gear chain on a bicycle that translates pedaling motion from a small, fast-moving gear into the motion of a much larger wheel. “Electrical frequency dividers used widely in electronics can work at frequencies no higher than 50 to 100 GHz. Our new architecture is a hybrid electro-optical ‘gear chain’ that stabilizes a common microwave electrical oscillator with optical references at much higher frequencies in the range of terahertz or trillions of cycles per second,” Li says.

The optical reference used by the researchers is a laser that, to the naked eye, looks like a tiny disk. At only 6 mm in diameter, the device is very small, making it particularly useful in compact photonics devices—electronic-like devices powered by photons instead of electrons, says Scott Diddams, physicist and project leader at the National Institute of Standards and Technology and a coauthor on the study.

“There are always tradeoffs between the highest performance, the smallest size, and the best ease of integration. But even in this first demonstration, these optical oscillators have many advantages; they are on par with, and in some cases even better than, what is available with widespread electronic technology,” Vahala says.

Academics should not remain silent on hacking : Nature News & Comment

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Academics should not remain silent on hacking

The revelation that US and British spy agencies have undermined a commonly used encryption code should alarm researchers, says Charles Arthur.

Secrecy doesn’t come naturally to journalists, but sometimes it is thrust upon us. Earlier this year, there was a room in The Guardian‘s offices in London that nobody could enter alone. On a table outside by a security guard was a tidy collection of phones and other devices; nothing electronic was allowed. Inside were a coffee maker, a shredder, some paper and a few computers. All were brand new; none had ever been connected to the Internet. None ran Microsoft Windows. All were encrypted; each required two passwords, held by different people.

This is where the biggest news stories of this year lived — away from the Internet. This was where The Guardian analysed the ‘Snowden files’ (classified documents released to the press by former US National Security Agency (NSA) contractor Edward Snowden). These revealed, among other things, that the NSA and the United Kingdom’s GCHQ were running enormous efforts to crack encrypted communications online, and that they had worked to undermine the strength of encryption standards such as that used — and recommended — by the US National Institute of Standards and Technology (NIST). (The computers sadly are no more — smashed in The Guardian basement on the orders of the British government.)

NIST’s standard for random numbers used for cryptography, published in 2006, had been weakened by the NSA. Companies such as banks and financial institutions that rely on encryption to guarantee customer privacy depend on this standard. The nature of the subversions sounds abstruse: the random-number generator, the ‘Dual EC DRBG‘ standard, had been hacked by the NSA so that its output would not be as random as it should have been. That might not sound like much, but if you are trying to break an encrypted message, the knowledge that it is hundreds or thousands of times weaker than advertised is a great encouragement.

It was, to be frank, a big deal. In the world’s universities, computer scientists and mathematicians spend their careers trying to develop secure systems, and yet here was evidence of a systematic — and successful — attempt to undermine that work. Executives at companies such as Google, Yahoo, Facebook and Microsoft, which discovered that their internal networks were being tapped and their systems infiltrated, were furious. But a few isolated shouts of protest aside, the academic community has largely been silent.

That’s disappointing. Academia is where we expect to hear the free flow of ideas and opinions. Yet it has been the commercial companies that have made the most noise — because the revelations threaten trust in their businesses. Don’t academics also see the threat to open expression, and to the flow of dissident ideas from countries where people might fear that their communications are being tapped and, even if encrypted, cracked?

“Academics in cryptography and security should make themselves a promise: ‘we won’t get fooled again.’”

Some get it. Ross Anderson, a security researcher at the University of Cambridge, UK, has been highly critical and outspoken. When I spoke to him in September, soon after the NIST revelation, he called it “a wake-up call for a lot of people” and added: “This has been a 9/11 moment for the community, and it’s great that some people are beginning to wake up.”

Kenneth White, principal scientist at health-information company Social & Scientific Systems in Silver Spring, Maryland, says: “Just a year ago, such a story would have been derogated by most of my colleagues as unwarranted suspicion at best and outright paranoia at worst. But here we are.”

Anderson has an explanation for the muted response: he says that a number of British university departments have been quietly coerced by the GCHQ. The intelligence-gathering agency has a substantial budget, and ropes in academics by offering access to funds that ensures their silence on sensitive matters, Anderson says. (If that sounds like paranoia, then see above.)

I have not been able to confirm his claims, but what are the alternatives? One is that the academics are simply too busy going back over their own work looking to see if they agree with the claimed weaknesses. The other is that they simply don’t care enough.

For those who do care, White and Matthew Green, who teaches cryptography at Johns Hopkins University in Baltimore, Maryland, have embarked on an ambitious effort to clean up the mess — one that needs help.

They have created a non-profit organization called OpenAudit.org, which aims to recruit experts to provide technical assistance for security projects in the public interest, especially open-source security software. A similar effort initiated by White and Green is checking the open-source software called TrueCrypt, which is widely used to lock down hard drives during foreign travel (see go.nature.com/nsvdjh).

Concerns over the security of the NIST Dual EC DRBG standard were raised in 2007, but too few academics spoke out then. The events of 2013 must make them rethink. Cryptography rarely reaches the headlines, but now it has done so for all the wrong reasons. For 2014, academics working in cryptography and security should make themselves a promise: ‘We won’t get fooled again.’ And most of all, ‘We won’t go down quietly.’

Single photon detected but not destroyed.

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First instrument built that can witness the passage of a light particle without absorbing it.

Physicists have seen a single particle of light and then let it go on its way. The feat was possible thanks to a new technique that, for the first time, detects optical photons without destroying them. The technology could eventually offer perfect detection of photons, providing a boost to quantum communication and even biological imaging.

Plenty of commercially available instruments can identify individual light particles, but these instruments absorb the photons and use the energy to produce an audible click or some other signal of detection.

Quantum physicist Stephan Ritter and his colleagues at the Max Planck Institute of Quantum Optics in Garching, Germany, wanted to follow up on a 2004 proposal of a nondestructive method for detecting photons. Instead of capturing photons, this instrument would sense their presence, taking advantage of the eccentric realm of quantum mechanics in which particles can exist in multiple states and roam in multiple places simultaneously.

Ritter and his team started with a pair of highly reflective mirrors separated by a half-millimeter-wide cavity. Then they placed a single atom of rubidium in the cavity to function as a security guard. They chose rubidium because it can take on two distinct identities, which are determined by the arrangement of its electrons. In one state, it’s a 100 percent effective sentry, preventing photons from entering the cavity. In the other, it’s a totally useless lookout, allowing photons to enter the cavity. When photons get in, they bounce back and forth about 20,000 times before exiting.

The trick was manipulating the rubidium so that it was in a so-called quantum superposition of these two states, allowing one atom to be an overachiever and a slacker at the same time. Consequently, each incoming photon took multiple paths simultaneously, both slipping into the cavity undetected and being stopped at the door and reflected away. Each time the attentive state of the rubidium turned away a photon, a measurable property of the atom called its phase changed. If the phases of the two states of the rubidium atom differed, the researchers knew that the atom had encountered a photon.

To confirm their results, the researchers placed a conventional detector outside the apparatus to capture photons after their rubidium rendezvous, the team reports November 14 in Science.

“It’s a very cool experiment,” says Alan Migdall, who leads the quantum optics group at the National Institute of Standards and Technology in Gaithersburg, Md. But he warns that identifying photons without destroying them does not mean that the outgoing photon is the same as it was prior to detection. “You’ve pulled some information out of it, so you do wind up affecting it,” he says. Ritter says he expects the photons’ properties are largely unchanged, but he acknowledges that his team needs to perform more measurements to confirm that hypothesis.

Ritter notes that no photon detector is perfect, and his team’s is no exception: It failed to detect a quarter of incoming photons, and it absorbed a third of them. But he says the power of the technique is that, for many applications of single-photon detectors, each detector wouldn’t have to be perfect. Ritter envisions a nested arrangement of improved detectors that, as long as they did not absorb photons, would almost guarantee that every photon is counted. Ultimately, that could benefit fields such as medicine and molecular biology, in which scientists require precise imaging of objects in low-light environments.

Waxing Innovative: Researchers Pump Up Artificial Muscles Using Paraffin.

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artificial-muscle-advance_1

 

When Scientific American heard from chemist Ray Baughman a year ago, he and his international team of nanotechnologists had taken artificial-muscle technology to the next level. Their innovation relied on spinning lengths of carbon nanotubes into buff yarns whose twisting and untwisting mimicked natural muscles found in an elephant’s trunk or a squid’s tentacles.

Now the researchers are reporting a new artificial muscle–building technique that makes their carbon nanotube yarns several times faster and more powerful. These qualities could help deliver on the technology’s promise of developing compact, lightweight actuators for robots, exoskeletons and other mechanical devices, although several challenges remain.

The latest breakthrough comes from infusing the carbon nanotube yarns with paraffin wax that expands when heated, enabling the artificial muscles to lift more than 100,000 times their own weight and generate 85 times more mechanical power during contraction than mammalian skeletal muscles of comparable size, according to the researchers, whose latest work is published in the November 16 issue of Science.

The previous-generation artificial muscles were electrochemical and functioned like a supercapacitor. When a charge was injected into the carbon nanotube yarn, ions from a liquid electrolyte diffused into the yarn, causing it to expand in volume and contract in length, says Baughman, director of the University of Texas at Dallas‘s Alan G. MacDiarmid NanoTech Institute. Unfortunately, using an electrolyte limited the temperature range in which the muscle could function. At colder temperatures the electrolyte would solidify, slowing down the muscle; if too hot, the electrolyte would degrade. It also needed a container, which added weight to the artificial-muscle system.

The wax eliminates the need for an electrolyte, making the artificial muscle lighter, stronger and more responsive. When heat or a light pulse is applied to a wax-impregnated yarn about 200 microns in diameter (roughly twice that of a human hair), the wax melts and expands. In about 25 milliseconds this expansion creates pressure causing the yarn’s individual nanotube threads to twist and the yarn’s length to contract. Any weightlifter will tell you that the success of any muscle—artificial or natural—depends in part on the degree of this contraction. Depending on the force exerted, the Baughman team’s muscle strands could contract by up to 10 percent.

Muscles are also judged by the weight they can lift relative to their size. “Our muscles can lift about 200 times the weight of a similar-size natural muscle,” Baughman says, adding that the wax-infused artificial muscles can also generate 30 times the maximum power of their electrolyte-powered predecessors.

The researchers’ latest artificial muscles move the technology closer to commercialized products such as environmental sensors, aerospace materials and even textiles that take can take advantage of nanoscale actuators, University of Cincinnati mechanical engineering professor Mark Schulz, wrote in a related SciencePerspectives article. This new artificial muscle outperforms existing ones, allowing possible applications such as linear and rotary motors; it also might replace biological muscle tissue if biocompatibility can be established, he adds.

However, Schulz points out—and Baughman is quick to acknowledge—that even this new crop of artificial muscles faces many challenges before they can be a practical alternative to mini–electric motors in many of the products we buy. Despite their improvements, the latest artificial muscles are for the most part inefficient and limited in the combinations of force, motion and speed they can generate, according to Schulz.

Indeed, these new artificial muscles operate at about 1 percent efficiency, a number Baughman and his colleagues want to increase at least 10-fold. An option for improving efficiency is to use a chemical fuel rather than electricity to power the muscles. “One way to compensate for a lack of efficiency is to use fuel like methanol instead of a battery,” he says. “You could store more than 20 percent more energy in a fuel like methanol than you can in a battery.”

Another challenge is that the artificial muscles must be heated and cooled to contract and release, respectively. Short lengths of yarn can cool on their own in a matter of seconds, but longer pieces would need to be actively cooled using water or air, otherwise the muscle would not relax. “Or you’d need [to use a] material that doesn’t require thermal actuation,” Baughman says. “If you keep making the [carbon nanotube] yarn longer and longer, your cooling rate increases.”

This issue of scale poses perhaps the greatest challenge. A one-millimeter length of artificial muscle can lift about 50 grams, according to Baughman. That means lifting several tons would require a greater length of carbon nanotube yarn than is practical. “We’d like our artificial muscles to be used in exoskeletons that help workers or soldiers lift objects weighing tons,” he says. But the researchers are still working out ways to pack enough yarn to perform such tasks into the length of an exoskeletal limb.

Carbon nanotube artificial muscles are more likely to first appear in products requiring only short lengths. Baughman envisions artificial muscles used in a catheter for minimally invasive surgery, “where you want to have lots of functionality on the end of the catheter to do surgical manipulations.” Another application with flex appeal—”smart” fabrics that can automatically react to their environments, becoming more or less porous when they detect heat or harmful chemicals in the air.

 

Source: scientificamerican.com