Graphene Is Strongest Material in the World Even with Defects

Graphene remains the strongest material ever measured and, as Professor Hone once put it, so strong that "it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.” —Illustration by Andrew Shea for Columbia Engineering

In a new study, published in Science May 31, 2013, Columbia Engineering researchers demonstrate that graphene, even if stitched together from many small crystalline grains, is almost as strong as graphene in its perfect crystalline form. This work resolves a contradiction between theoretical simulations, which predicted that grain boundaries can be strong, and earlier experiments, which indicated that they were much weaker than the perfect lattice.

Graphene consists of a single atomic layer of carbon, arranged in a honeycomb lattice. “Our first Science paper, in 2008, studied the strength graphene can achieve if it has no defects—its intrinsic strength,” says James Hone, professor of mechanical engineering, who led the study with Jeffrey Kysar, professor of mechanical engineering. “But defect-free, pristine graphene exists only in very small areas. Large-area sheets required for applications must contain many small grains connected at grain boundaries, and it was unclear how strong those grain boundaries were. This, our second Science paper, reports on the strength of large-area graphene films grown using chemical vapor deposition (CVD), and we’re excited to say that graphene is back and stronger than ever.”

The study verifies that commonly used methods for post-processing CVD-grown graphene weaken grain boundaries, resulting in the extremely low strength seen in previous studies. The Columbia Engineering team developed a new process that prevents any damage of graphene during transfer. “We substituted a different etchant and were able to create test samples without harming the graphene,” notes the paper’s lead author, Gwan-Hyoung Lee, a postdoctoral fellow in the Hone lab. “Our findings clearly correct the mistaken consensus that grain boundaries of graphene are weak. This is great news because graphene offers such a plethora of opportunities both for fundamental scientific research and industrial applications.”

                                              Profs. James Hone and Jeffrey Kysar
In its perfect crystalline form, graphene (a one-atom-thick carbon layer) is the strongest material ever measured, as the Columbia Engineering team reported in Science in 2008—so strong that, as Hone observed, “it would take an elephant, balanced on a pencil, to break through a sheet of graphene the thickness of Saran Wrap.” For the first study, the team obtained small, structurally perfect flakes of graphene by mechanical exfoliation, or mechanical peeling, from a crystal of graphite. But exfoliation is a time-consuming process that will never be practical for any of the many potential applications of graphene that require industrial mass production.

Currently, scientists can grow sheets of graphene as large as a television screen by using chemical vapor deposition (CVD), in which single layers of graphene are grown on copper substrates in a high-temperature furnace. One of the first applications of graphene may be as a conducting layer in flexible displays.

“But CVD graphene is ‘stitched’ together from many small crystalline grains—like a quilt—at grain boundaries that contain defects in the atomic structure,” Kysar explains. “These grain boundaries can severely limit the strength of large-area graphene if they break much more easily than the perfect crystal lattice, and so there has been intense interest in understanding how strong they can be.”

The Columbia Engineering team wanted to discover what was making CVD graphene so weak. In studying the processing techniques used to create their samples for testing, they found that the chemical most commonly used to remove the copper substrate also causes damage to the graphene, severely degrading its strength.

WATCH VIDEO
Click on the Video to watch Prof. James Hone take us on a tour of his synthesis lab in the Northwest Corner Building, where he grows graphene and nanotubes.

Their experiments demonstrated that CVD graphene with large grains is exactly as strong as exfoliated graphene, showing that its crystal lattice is just as perfect. And, more surprisingly, their experiments also showed that CVD graphene with small grains, even when tested right at a grain boundary, is about 90% as strong as the ideal crystal.

“This is an exciting result for the future of graphene, because it provides experimental evidence that the exceptional strength it possesses at the atomic scale can persist all the way up to samples inches or more in size,” says Hone. “This strength will be invaluable as scientists continue to develop new flexible electronics and ultrastrong composite materials.”

Strong, large-area graphene can be used for a wide variety of applications such as flexible electronics and strengthening components—potentially, a television screen that rolls up like a poster or ultrastrong composites that could replace carbon fiber. Or, the researchers speculate, a science fiction idea of a space elevator that could connect an orbiting satellite to Earth by a long cord that might consist of sheets of CVD graphene, since graphene (and its cousin material, carbon nanotubes) is the only material with the high strength-to-weight ratio required for this kind of hypothetical application.

The team is also excited about studying 2D materials like graphene. “Very little is known about the effects of grain boundaries in 2D materials,” Kysar adds. “Our work shows that grain boundaries in 2D materials can be much more sensitive to processing than in 3D materials. This is due to all the atoms in graphene being surface atoms, so surface damage that would normally not degrade the strength of 3D materials can completely destroy the strength of 2D materials. However with appropriate processing that avoids surface damage, grain boundaries in 2D materials, especially graphene, can be nearly as strong as the perfect, defect-free structure.”

The study was supported by grants from the Air Force Office of Scientific Research and the National Science Foundation.

—by Holly Evarts

Source: Columbia University

Grad Student Solves 30-Year-Old Physics Problem

                    Emilie Huffman, second year PhD student in physics. Credit: Duke University

Sometimes an age-old question just needs a fresh set of eyes.

That was the case in Duke’s physics department, where a graduate student and professor recently resolved a calculating dilemma that has vexed computational physicists for decades.

Emilie Huffman is a second-year PhD student from Charlotte, North Carolina. Last spring she began working with Shailesh Chandrasekharan, an associate professor and the director of graduate studies in physics, on what’s known as a sign problem.

Chandrasekharan is a theoretical nuclear and particle physicist who specializes in solving sign problems, which arise when one uses certain computational algorithms to calculate the behavior of large numbers of particles called fermions.

“Almost all the matter we know of are made with fermions,” Chandrasekharan said. “As building blocks of matter, it’s very important to be able to do calculations with them.”

But calculations of such complexity get tricky, and sign problems make it easy for wrong results to surface.

“It’s a very broad problem that affects almost all fields of physics involving quantum mechanics with strong correlations, where Monte Carlo methods are essential to perform calculations,” Chandrasekharan said.

Some in the field have simply moved on since the 1980s, leaving interesting questions plagued by sign problems unexplored. Other scientists have found workarounds and approximations. Very few, including Chandrasekharan, have tried to figure out solutions through the years. Huffman began work to expand on one of her advisor’s solutions, involving a grouping concept called fermion bags, and apply them to a new class of problems.

“She finally figured out a nice formula,” Chandrasekharan said. “Although the formula is quite simple and elegant, I couldn’t guess it.”

“In physics, often there’s a truth, and if you’re hitting on the right truth, everything starts falling into place.” Chandrasekharan says that’s what happened when he began applying Huffman’s formula to a class of problems.

Their paper appeared recently in the journal Physical Review B’s Rapid Communications.

“Now that I have a solution, I can begin to apply it,” Huffman said. Starting with condensed matter physics, Huffman plans to apply her solution to various questions that have been stymied by sign problems. “I can use this solution to study properties of graphene,” she said, referring to the single-layer carbon that has been touted as the strongest material in the world. Many puzzles remain in the field, especially involving multi-layer graphene sheets.

Wherever she turns her attention next, it’s clear Huffman has a promising career ahead.

Citation: “Solution to sign problems in half-filled spin-polarized electronic systems,” Emilie Huffman and Shailesh Chandrasekharan. Physical Review B Rapid Communications, March 12, 2014. DOI: 10.1103/PhysRevB.89.111101.

Source: Duke University

String field theory could be the foundation of quantum mechanics: Connection could be huge boost to string theory

Artist's abstraction (stock illustration). Credit: © agsandrew / Fotolia

Two USC researchers have proposed a link between string field theory and quantum mechanics that could open the door to using string field theory -- or a broader version of it, called M-theory -- as the basis of all physics.

"This could solve the mystery of where quantum mechanics comes from," said Itzhak Bars, USC Dornsife College of Letters, Arts and Sciences professor and lead author of the paper.

Bars collaborated with Dmitry Rychkov, his Ph.D. student at USC. The paper was published online on Oct. 27 by the journal Physics Letters.

Rather than use quantum mechanics to validate string field theory, the researchers worked backwards and used string field theory to try to validate quantum mechanics.

In their paper, which reformulated string field theory in a clearer language, Bars and Rychov showed that a set of fundamental quantum mechanical principles known as "commutation rules'' may be derived from the geometry of strings joining and splitting.

"Our argument can be presented in bare bones in a hugely simplified mathematical structure," Bars said. "The essential ingredient is the assumption that all matter is made up of strings and that the only possible interaction is joining/splitting as specified in their version of string field theory."

Physicists have long sought to unite quantum mechanics and general relativity, and to explain why both work in their respective domains. First proposed in the 1970s, string theory resolved inconsistencies of quantum gravity and suggested that the fundamental unit of matter was a tiny string, not a point, and that the only possible interactions of matter are strings either joining or splitting.

Four decades later, physicists are still trying to hash out the rules of string theory, which seem to demand some interesting starting conditions to work (like extra dimensions, which may explain why quarks and leptons have electric charge, color and "flavor" that distinguish them from one another).

At present, no single set of rules can be used to explain all of the physical interactions that occur in the observable universe.

On large scales, scientists use classical, Newtonian mechanics to describe how gravity holds the moon in its orbit or why the force of a jet engine propels a jet forward. Newtonian mechanics is intuitive and can often be observed with the naked eye.

On incredibly tiny scales, such as 100 million times smaller than an atom, scientists use relativistic quantum field theory to describe the interactions of subatomic particles and the forces that hold quarks and leptons together inside protons, neutrons, nuclei and atoms.

Quantum mechanics is often counterintuitive, allowing for particles to be in two places at once, but has been repeatedly validated from the atom to the quarks. It has become an invaluable and accurate framework for understanding the interactions of matter and energy at small distances.

Quantum mechanics is extremely successful as a model for how things work on small scales, but it contains a big mystery: the unexplained foundational quantum commutation rules that predict uncertainty in the position and momentum of every point in the universe.

"The commutation rules don't have an explanation from a more fundamental perspective, but have been experimentally verified down to the smallest distances probed by the most powerful accelerators. Clearly the rules are correct, but they beg for an explanation of their origins in some physical phenomena that are even deeper," Bars said.

The difficulty lies in the fact that there's no experimental data on the topic -- testing things on such a small scale is currently beyond a scientist's technological ability.

Source: University of Southern California

Strange materials cropping up in condensed matter laboratories

A conformal field theory in condensed matter (labelled CFT) gets a hand from string theory – the string theory hand has an extra dimension and a black hole in it. Credit: Image courtesy of Perimeter Institute for Theoretical Physics

Subir Sachdev, William Witczak-Krempa, and Erik Sørensen are condensed matter physicists. They study exotic but tangible systems, such as superfluids. And their latest paper about one such system has a black hole in it.

How did a black hole get into a condensed matter paper? "Well, it's a long story," says Sachdev, who is a professor at Harvard and a Distinguished Visiting Research Chair at Perimeter Institute.

It's a long story, he might add, that in a way starts with him: he was one of the first condensed matter physicists to venture into the strange land of string theory, where the black holes live. But that is getting ahead of the tale.

"Let's start here," Sachdev says. "Condensed matter physicists study the behaviour of electrons in many materials -- semiconductors, metals, and exotic materials like superconductors."

Normally, these physicists can model the behaviour of a material as if electrons were moving freely around inside it. Even if that's not what's actually happening, because of complex interactions, it makes the model easy to understand and the calculations easier to do. Electrons (and occasionally other particles) used in this kind of short-hand model are called quasi-particles.

However, there are a handful of systems that cannot be described by considering electrons (or any other kind of quasi-particle) moving around.

"What we try to do is understand a quantum system where you have electricity without electrons," says Sachdev. "Of course, the system does have electrons in it, but the behaviour of the system doesn't look like electrons moving at all. What you see is not even particles, but some lumps of quantum excitations that are doing strange quantum things."

"Without quasi-particles, it's a mess," says William Witczak-Krempa. Witczak-Krempa, a Perimeter postdoctoral fellow, is also a condensed matter theorist who collaborated with Sachdev on the paper. "It's this quantum fuzzball of stuff."

Describing such a fuzzball system is a challenge -- but it's crucial to understanding many modern materials, including superfluids and high-temperature superconductors. The broad problem of how to model systems without quasi-particles has been stumping condensed matter theorists for decades.

"What we decided to do was look at a simple case of such an electricity-without-electrons system," says Witczak-Krempa. "That turns out to be a quantum phase transition between a superfluid and an insulator."

A fair amount of work had been done on such systems, such that the team was able to make progress modelling the system using the traditional mathematical tools of condensed matter. Sachdev and Witczak-Krempa worked with Erik Sørensen of McMaster University on this aspect of their paper. Sørensen used a computer simulation -- specifically, a quantum Monte Carlo simulation -- to predict how conductivity should change with temperature and frequency as a superfluid turns into an insulator.

"This frequency dependence tells us how the quantum fluid behaves in time. This dynamic behaviour is notoriously hard to study using standard methods, including quantum Monte Carlo simulations," says Witczak-Krempa. "Erik's work was a huge computational achievement. It took months of processing time. And, in the end, the results still needed to be converted into a form that can be compared with experiments. This is where we tried something new."

To perform this conversion, Sachdev and Witczak-Krempa tackled the same system from a different angle: string theory. (Here, they build on Sachdev's previous work with Perimeter Faculty member Robert Myers and one of his graduate students, Ajay Singh.) One of the pillars of string theory is that certain quantum field theories (technically known as conformal field theories) can be translated into a theory of gravity with one extra dimension.

Sachdev explains where the extra dimension comes in. Wiggling his fingers above the tabletop, he conjures strings moving through the air.

"In certain configurations, the strings all end on a kind of membrane," he says, tapping his fingertips on the table's surface. "You might ask yourself: if you were living on the membrane [the table surface] -- and you didn't know about the extra dimensions where the strings were, what would you see?"

He answers himself: "Only the ends of the strings. They would look like particles. What's amazing is that string theorists found that the theories that you'd use to define the ends of the strings on the membrane are remarkably like the theory we want to use to describe our system."

The quantum field theory describing Sachdev and Witczak-Krempa's "fuzzball" system shares many fundamental properties with the conformal field theories associated with string theory -- so many that the researchers were able to map the two-dimensional field theory into a three-dimensional theory of gravity.

"We ended up studying the physics of this alternate reality," says Witczak-Krempa. "Using this technique, we were able to translate a very hard problem into a fairly easy one." Albeit a fairly easy problem involving a black hole.

"We wanted to look at the physics of the boundary -- the physics at the table top," says Witczak-Krempa. "But we wanted to heat it up a bit -- give it a finite temperature. It turns out that the natural way of doing this is to invoke a black hole." Really?

"There are various ways of developing an intuition about that," he says. "For instance, you can remember that the black hole will release Hawking radiation. The Hawking radiation escapes and eventually hits the boundary where the system lives, and heats it up."

Witczak-Krempa admits it's unorthodox: "Most condensed matter people would go: 'Why is there a black hole in this paper?' It's crazy. But what's even crazier is that this mathematical machinery works quite well. It gives you answers that make a lot of sense. You can compare them directly with Erik's Monte Carlo results, and they check out."

It's the first time results from a traditional large-scale condensed matter simulation have been compared to results from the new string theory approach.

Sachdev is cautiously thrilled: "There are a couple of issues we don't fully understand and one discrepancy we wish we understood better, but in general it's worked extremely well. It's progress on something I've been thinking about for more than 20 years. And now we finally have a theory that is perhaps not complete, but is encouragingly successful."

What's more, string theory has finally produced a set of physical predictions that experimentalists can go check. Sachdev and Witczak-Krempa are hoping that an experimental team will try soon.

"Let's see what happens," says Sachdev. "We're pushing string theory to a new regime. Whatever happens, we will learn more."

Source: Perimeter Institute for Theoretical Physics

Einstein's 'spooky' theory may lead to ultra-secure Internet

Could new research into Einstein's 'spooky action at a distance' pave the way for a new ultra-secure quantum Internet? Credit: © Serg Nvns / Fotolia

Einstein's skepticism about quantum mechanics may lead to an ultra-secure Internet, suggests a new paper by researchers from Swinburne University of Technology and Peking University.

Associate Professor Margaret Reid from Swinburne's Centre for Quantum and Optical Science said Einstein's reservations about quantum mechanics were highlighted in a phenomenon known as "'spooky' action at a distance."

In 1935, Einstein and researchers highlighted a 'spooky' theory in quantum mechanics, which is the strange way entangled particles stay connected even when separated by large distances.

"Until now the real application of this has been for messages being shared between two people securely without interception, regardless of the spatial separation between them," Professor Reid said.

"In this paper, we give theoretical proof that such messages can be shared between more than two people and may provide unprecedented security for a future quantum Internet."

In the 1990s, scientists realised you can securely transmit a message through encrypting and using a shared key generated by Einstein's strange entanglement to decode the message from the sender and receiver. Using the quantum key meant the message was completely secure from interception during transmission.

Sending Einstein's entanglement to a larger number of people means the key can be distributed among all the receiving parties, so they must collaborate to decipher the message, which Professor Reid said makes the message even more secure.

"We found that a secure message can be shared by up to three to four people, opening the possibility to the theory being applicable to secure messages being sent from many to many.

"The message will also remain secure if the devices receiving the message have been tampered with, like if an iPhone were hacked, because of the nature of Einstein's spooky entanglement.

"Discovering that it can be applied to a situation with more parties has the potential to create a more secure Internet -- with less messages being intercepted from external parties."

Source: Swinburne University of Technology

Tremors of the Big Bang: First direct evidence of cosmic inflation

Gravitational waves from inflation generate a faint but distinctive twisting pattern in the polarization of the cosmic microwave background, known as a "curl" or B-mode pattern. For the density fluctuations that generate most of the polarization of the CMB, this part of the primordial pattern is exactly zero. Shown here is the actual B-mode pattern observed with the BICEP2 telescope, which is consistent with the pattern predicted for primordial gravitational waves. The line segments show the polarization strength and orientation at different spots on the sky. The red and blue shading shows the degree of clockwise and anti-clockwise twisting of this B-mode pattern. Credit: BICEP2 Collaboration

Almost 14 billion years ago, the universe we inhabit burst into existence in an extraordinary event that initiated the Big Bang. In the first fleeting fraction of a second, the universe expanded exponentially, stretching far beyond the view of our best telescopes. All this, of course, was just theory.

Researchers from the BICEP2 collaboration today announced the first direct evidence for this cosmic inflation. Their data also represent the first images of gravitational waves, or ripples in space-time. These waves have been described as the "first tremors of the Big Bang." Finally, the data confirm a deep connection between quantum mechanics and general relativity.

"Detecting this signal is one of the most important goals in cosmology today. A lot of work by a lot of people has led up to this point," said John Kovac (Harvard-Smithsonian Center for Astrophysics), leader of the BICEP2 collaboration.

These groundbreaking results came from observations by the BICEP2 telescope of the cosmic microwave background -- a faint glow left over from the Big Bang. Tiny fluctuations in this afterglow provide clues to conditions in the early universe. For example, small differences in temperature across the sky show where parts of the universe were denser, eventually condensing into galaxies and galactic clusters.

Since the cosmic microwave background is a form of light, it exhibits all the properties of light, including polarization. On Earth, sunlight is scattered by the atmosphere and becomes polarized, which is why polarized sunglasses help reduce glare. In space, the cosmic microwave background was scattered by atoms and electrons and became polarized too.

"Our team hunted for a special type of polarization called 'B-modes,' which represents a twisting or 'curl' pattern in the polarized orientations of the ancient light," said co-leader Jamie Bock (Caltech/JPL).

Gravitational waves squeeze space as they travel, and this squeezing produces a distinct pattern in the cosmic microwave background. Gravitational waves have a "handedness," much like light waves, and can have left- and right-handed polarizations.

"The swirly B-mode pattern is a unique signature of gravitational waves because of their handedness. This is the first direct image of gravitational waves across the primordial sky," said co-leader Chao-Lin Kuo (Stanford/SLAC).

The team examined spatial scales on the sky spanning about one to five degrees (two to ten times the width of the full Moon). To do this, they traveled to the South Pole to take advantage of its cold, dry, stable air.

"The South Pole is the closest you can get to space and still be on the ground," said Kovac. "It's one of the driest and clearest locations on Earth, perfect for observing the faint microwaves from the Big Bang."

They were surprised to detect a B-mode polarization signal considerably stronger than many cosmologists expected. The team analyzed their data for more than three years in an effort to rule out any errors. They also considered whether dust in our galaxy could produce the observed pattern, but the data suggest this is highly unlikely.

"This has been like looking for a needle in a haystack, but instead we found a crowbar," said co-leader Clem Pryke (University of Minnesota).

When asked to comment on the implications of this discovery, Harvard theorist Avi Loeb said, "This work offers new insights into some of our most basic questions: Why do we exist? How did the universe begin? These results are not only a smoking gun for inflation, they also tell us when inflation took place and how powerful the process was."

BICEP2 is the second stage of a coordinated program, the BICEP and Keck Array experiments, which has a co-PI structure. The four PIs are John Kovac (Harvard), Clem Pryke (UMN), Jamie Bock (Caltech/JPL), and Chao-Lin Kuo (Stanford/SLAC). All have worked together on the present result, along with talented teams of students and scientists. Other major collaborating institutions for BICEP2 include the University of California at San Diego, the University of British Columbia, the National Institute of Standards and Technology, the University of Toronto, Cardiff University, Commissariat à l'Energie Atomique.

BICEP2 is funded by the National Science Foundation (NSF). NSF also runs the South Pole Station where BICEP2 and the other telescopes used in this work are located. The Keck Foundation also contributed major funding for the construction of the team's telescopes. NASA, JPL, and the Moore Foundation generously supported the development of the ultra-sensitive detector arrays that made these measurements possible.

Technical details and journal papers can be found on the BICEP2 release website: http://bicepkeck.org

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

Source: Harvard–Smithsonian Center for Astrophysics

Law of physics governs airplane 'evolution': Constructal law explains progression of passenger jets, sets guidelines for future aircraft

This graph shows how -- as the years have passed -- bigger and bigger airplanes have joined the ranks of their behemoth brothers. Credit: Adrian Bejan

Researchers believe they now know why the supersonic trans-Atlantic Concorde aircraft went the way of the dodo -- it hit an evolutionary cul-de-sac.

In a new study, Adrian Bejan, professor of mechanical engineering and materials science at Duke University, shows that a law of physics he penned more than two decades ago helps explain the evolution of passenger airplanes from the small, propeller-driven DC-3s of yore to today's behemoth Boeing 787s. The analysis also provides insights into how aerospace companies can develop successful future designs.

The Concorde, alas, was too far from the curve of these good designs, Bejan says. The paper appears online July 22, in the Journal of Applied Physics.

"The evolution of Earth's species occurred on a timescale far too large for humans to witness," said Bejan. "But the evolution of our use of technology and airplanes to transport people and goods has taken place in little more than a single lifetime, making it visible to those who look. Evolution is a universal phenomenon encompassing technology, river basins and animal design alike, and it is rooted in physics as the constructal law."

The constructal law was developed by Bejan in 1996 and states that for a system to survive, it must evolve to increase its access to flow. For example, the human vascular system has evolved to provide blood access to flow through a network of a few large arteries and many small capillaries. River systems, tree branches and modern highway and road networks show the same forces at work, he says.

In the case of commercial aircraft, designs have evolved to allow more people and goods to flow across the face of Earth. Constructal law has also dictated the main design features needed for aircraft to succeed; the engine mass has remained proportional to the body size, the wing size has been tied to the fuselage length, and the fuel load has grown in step with the total weight.

"The same design features can be seen in any large land animal," said Bejan. "Larger animals have longer lifespans and travel farther distances, just as passenger airplanes have been designed to do. For example, the ratio of the engine to aircraft size is analogous to the ratio of a large animal's total body size to its heart, lungs and muscles."

To apply his theories to airplane design, Bejan teamed up with Jordan Charles, a researcher and development engineer, and Sylvie Lorente, a professor of civil engineering at the University of Toulouse, to mine the historical databases of successful commercial aircraft. As they plotted thousands of statistics including year of introduction, size, cruising speed, engine weight, fuel weight, range, wingspan and fuselage length, many patterns began to emerge.

But two in particular stood out.

In one chart, a clear curve tracks the increasing size of commercial airplanes through nearly a century of aviation. As time moves on, new commercial airliners come in all sizes but the biggest are joined by even bigger models. In another chart, the line that best tracks the relationship of body mass to airplane speeds is nearly identical to mass and speed statistics from various mammals, lizards, birds, insects and more. Evolutionary constraints found in nature, in other words, can be seen at work in the airline industry.

There was, however, one outlier on the chart -- the Concorde.

"The Concorde was too far off from the ratios that evolution has produced in passenger jets," explained Bejan, who points out that the doomed aircraft had limited passenger capacity, a low mass-to-velocity ratio, an off-the-charts fuselage-to-wingspan ratio, massive engines and poor fuel economy. "It would have had to adhere to the constructal design rules to succeed."

Bejan said this analysis shows that the aviation industry has done well with its designs over the decades, and that the trends dominating the industry are indeed the most efficient. They also reveal the general design parameters that future passenger aircraft should follow to succeed economically.

"This study gives the rough sketch of what airplane designs will put you in the game," said Bejan. "For design companies, it is money in the bank."

Jose Camberos, research aerospace engineer and lead of design space exploration at the Multidisciplinary Science & Technology Center of the Air Force Research Laboratory at Wright-Patterson Air Force Base in Dayton, Ohio, said that the work will hopefully give the field better insight into where the design of airplanes is going.

"There is definitely an analogy to be understood and articulated to explain why engines and airplanes are sized the way they currently are and how that has evolved," said Camberos, who was not involved with this study. "By looking at the development of aircraft in a larger context in these terms, it may be possible to gain insights into how best to achieve what nature has been able to accomplish already."

Source: Duke University

Quantum physics just got less complicated: Wave-particle duality and quantum uncertainty are same thing

Quantum physics says that particles can behave like waves, and vice versa. Researchers have now shown that this 'wave-particle duality' is simply the quantum uncertainty principle in disguise. Credit: Timothy Yeo / CQT, National University of Singapore; CC-BY

Here's a nice surprise: quantum physics is less complicated than we thought. An international team of researchers has proved that two peculiar features of the quantum world previously considered distinct are different manifestations of the same thing. The result is published 19 December in Nature Communications.

Patrick Coles, Jedrzej Kaniewski, and Stephanie Wehner made the breakthrough while at the Centre for Quantum Technologies at the National University of Singapore. They found that 'wave-particle duality' is simply the quantum 'uncertainty principle' in disguise, reducing two mysteries to one.

"The connection between uncertainty and wave-particle duality comes out very naturally when you consider them as questions about what information you can gain about a system. Our result highlights the power of thinking about physics from the perspective of information," says Wehner, who is now an Associate Professor at QuTech at the Delft University of Technology in the Netherlands.

The discovery deepens our understanding of quantum physics and could prompt ideas for new applications of wave-particle duality.

Wave-particle duality is the idea that a quantum object can behave like a wave, but that the wave behaviour disappears if you try to locate the object. It's most simply seen in a double slit experiment, where single particles, electrons, say, are fired one by one at a screen containing two narrow slits. The particles pile up behind the slits not in two heaps as classical objects would, but in a stripy pattern like you'd expect for waves interfering. At least this is what happens until you sneak a look at which slit a particle goes through -- do that and the interference pattern vanishes.

The quantum uncertainty principle is the idea that it's impossible to know certain pairs of things about a quantum particle at once. For example, the more precisely you know the position of an atom, the less precisely you can know the speed with which it's moving. It's a limit on the fundamental knowability of nature, not a statement on measurement skill. The new work shows that how much you can learn about the wave versus the particle behaviour of a system is constrained in exactly the same way.

Wave-particle duality and uncertainty have been fundamental concepts in quantum physics since the early 1900s. "We were guided by a gut feeling, and only a gut feeling, that there should be a connection," says Coles, who is now a Postdoctoral Fellow at the Institute for Quantum Computing in Waterloo, Canada.

It's possible to write equations that capture how much can be learned about pairs of properties that are affected by the uncertainty principle. Coles, Kaniewski and Wehner are experts in a form of such equations known as 'entropic uncertainty relations', and they discovered that all the maths previously used to describe wave-particle duality could be reformulated in terms of these relations.

"It was like we had discovered the 'Rosetta Stone' that connected two different languages," says Coles. "The literature on wave-particle duality was like hieroglyphics that we could now translate into our native tongue. We had several eureka moments when we finally understood what people had done," he says.

Because the entropic uncertainty relations used in their translation have also been used in proving the security of quantum cryptography -- schemes for secure communication using quantum particles -- the researchers suggest the work could help inspire new cryptography protocols.

In earlier papers, Wehner and collaborators found connections between the uncertainty principle and other physics, namely quantum 'non-locality' and the second law of thermodynamics. The tantalising next goal for the researchers is to think about how these pieces fit together and what bigger picture that paints of how nature is constructed.

Source: Centre for Quantum Technologies at the National University of Singapore