Even With Defects, Graphene Is Strongest Material in the World

In a new study, published in Science, 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."

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.

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.

Read more at Science Daily

First Glimpse of Moving Starlight

The entire cosmos is filled with light that has never been seen. Every star in every galaxy that’s ever existed in our universe has emitted starlight. Curious as it may sound, almost all of that light is still traveling through the cosmos. Yet remarkably enough, a group of researchers has managed to get a glimpse of this starlight as it’s still traveling.

This sea of photons, some newly created, some fantastically ancient, which surrounds everything is known as Extragalactic Background Light (or EBL for short). In a similar way to the Cosmic Microwave Background (CMB) — the leftover radiation from the big bang — measuring the EBL is rather important in cosmology.

Most recently, new research published by Alberto Dominguez, together with six co-authors, gives the best measurement ever made of this background light, showing how the EBL has varied over the past 5 billion years!

Measuring Light Before it Reaches You

Physicists consider light to be comprised of tiny, discreet packets of energy, referred to as photons. Photons that reach our eyes, we see. Whether emitted by shining stars, generated by computer screens, or reflected from surfaces, these photons allow us our view of the Universe. But unless they reach our eyes, we’d never even know they were there.

Consider that thought, and you might realize that our universe is actually filled with photons. Because space is mostly empty, most of the photons leaving a star like the Sun will never land on any surface. Only a small percentage illuminate planets like ours, and the number which reach planets around other stars is infinitesimal, compared to the total number of photons the Sun produces. Soon enough, these photons will actually leave the galaxy. Once they do, they become denizens of intergalactic space, with only a tiny chance of ever entering another galaxy.

Needless to say, seeing light while it’s still traveling is no easy task. In fact, it’s actually impossible to measure directly. In order to glimpse the EBL, Dominguez’s team needed to take some rather ingenious measures. They turned their attention to a type of galaxy known as a blazar.

Blazars are distant galaxies whose central supermassive black holes are pointed directly towards Earth. This means that intensely bright light emitted by those black holes is easy to spot, even from halfway across the Universe.

By looking at gamma rays emitted by those blazars — or more specifically, the attenuation of certain energies of gamma ray — the scientistss managed to accurately gauge what photons were in the intergalactic space between us and the blazars.

Gamma Ray Attenuation

Attenuation simply means that between us and the blazar, photons have been absorbed, meaning the light appears less intense than it should. The precise reason for this lies in the rather bizarre realm of quantum physics.

The universe at the quantum level, is a very strange place indeed. Einstein’s theory of relativity famously states that E = mc² — or in other words, mass and energy are two sides of the same coin. In deep space, photons are so numerous that they may collide with each other. When they do, if the combined energy of the two photons is high enough, they can spontaneously create matter (this is studied in a field known as two photon physics).

When photons create matter this way, they produce a pair of matter and anti-matter particles which then proceed to go their separate ways. Only photons with specific energies can interact in this way — so by looking at blazars and measuring which gamma ray wavelengths are attenuated, Dominguez and his colleagues could work backwards and find out which photons they were interacting with.

This gives an indirect measure of which photons were a part of the EBL that the blazar light traveled through. Because light only travels at a finite speed, looking at more distant blazars allows the EBL to be measured further away.

For a long time, this gamma ray attenuation had only ever been predicted. Until late last year, when observations taken with the Fermi gamma ray observatory confirmed that gamma rays from distant blazars are indeed absorbed before they reach us.

The Cosmic Gamma Ray Horizon

In order to actually measure the gamma ray attenuation, Dominguez and company first had to look at the blazars at lower energies, using a variety of different telescopes. Looking at x rays and other lower energy photons, they managed to calculate how bright the blazars should appear at gamma ray energies.

They then used several more telescopes to directly observe how bright the blazars are in gamma rays. The difference between the predicted and observed brightnesses gave the attenuation and, in turn, the EBL which would have caused that attenuation.

This research gives the first ever significant detection of a region of space known as the Cosmic Gamma Ray Horizon — the distance at which roughly one third of gamma rays at a certain specific energy have been absorbed.

By looking at the EBL over the past 5 billion years, cosmologists can learn about how galaxies change as the Universe ages. Whether or not ancient galaxies work the same way as modern ones is very important to our understanding of the Universe.

As it happens, the kinds of galaxies observed in the Universe today are responsible for most of the extragalactic background light over all time. Because there’s still a lot out there in the Universe which we don’t fully understand, it also sets a limit on any other light sources which we may not yet know about.

Read more at Discovery News

One of the Moon's Mysteries Solved: Origin of Mascon Basins

A mystery of the moon that imperiled astronauts and spacecraft on lunar missions has been solved by a Purdue University-led team of scientists as part of NASA's GRAIL mission.

Large concentrations of mass lurk on the lunar surface hidden like coral reefs beneath the ocean waves -- an unseen and devastating hazard. These concentrations change the gravity field and can either pull a spacecraft in or push it off course, sealing its fate to a crash on the face of the moon.

"In 1968 these mass concentrations were an unwelcome discovery as scientists prepared for the Apollo landings, and they have remained a mystery ever since," said Jay Melosh, a member of the Gravity Recovery and Interior Laboratory, or GRAIL, science team who led the research. "GRAIL has now mapped where they lay, and we have a much better understanding of how they developed. If we return to the moon, we can now navigate with great precision."

A better understanding of these features also adds clues to the moon's origin and evolution and will be useful in studying other planets where mass concentrations also are known to exist including Mars and Mercury, said Melosh, who is a distinguished professor of earth, atmospheric and planetary sciences and physics.

"We now know the ancient moon must have been much hotter than it is now and the crust thinner than we thought," he said. "For the first time we can figure out what size asteroids hit the moon by looking at the basins left behind and the gravity signature of the areas. We now have tools to figure out more about the heavy asteroid bombardment and what the ancient Earth may have faced."

The team confirmed the standing theory that the concentrations of mass were caused by massive asteroid impacts billions of years ago and determined how these impacts changed the density of material on the moon's surface and, in turn, its gravity field. A paper detailing the results will be published online by the journal Science on May 30.

In addition to Melosh, Purdue team members include Andrew Freed, associate professor of earth, atmospheric and planetary sciences, and graduate students Brandon Johnson and David Blair. Additional team members include Maria Zuber, GRAIL principal investigator and professor at the Massachusetts Institute of Technology; J. Andrews-Hanna of the Colorado School of Mines; S. Solomon of Columbia University; and the GRAIL Science Team.

"The explanation of mascons has eluded scientists for decades," Zuber said. "Since their initial discovery they have also been observed on Mars and Mercury, and by understanding their formation on the moon we have greatly advanced knowledge of how major impacts modified planetary crusts."

The mass concentrations form a target pattern with a gravity surplus at the bulls-eye surrounded by a ring of gravity deficit and an outer ring of gravity surplus. The team found that this pattern arises as a natural consequence of crater excavation, collapse and cooling following an impact.

The team determined that the increase in density and gravitational pull at the bulls-eye was caused by lunar material melted from the heat of the asteroid impact. The melting causes the material to become more concentrated, stronger and denser, and pulls in additional material from the surrounding areas, Melosh said.

The large asteroid impacts also caused big holes into which the surrounding lunar material collapsed. As the cool, strong lunar crust slid into the holes it bent downward, forming a rigid, curved edge that held down the material beneath it and prevented it from fully rebounding to its original surface height. This causes a ring with less gravitational pull because the mass is held farther below the surface, the top of which is what most influences the gravitational signature, he said.

The outer ring of increased gravitational pull comes from the added mass of the material ejected by the initial impact that then piles on top of the lunar surface.

The team combined expertise in specialized computer analysis methods called hydrocodes and finite element codes to create computer simulations that could show the physical changes occurring from microseconds to millions of years. The team analyzed the Freundlich-Sharanov and Humorum mascon basins.

Melosh is a pioneer in adapting computer hydrocodes -- computer programs originally created to analyze the flow of liquids -- to simulate how complex materials move when high-speed collisions occur, like that of a planetary collision. Hydrocodes can be used to study such phenomena on a time scale of microseconds to hours, but are not practical from time scales much longer than that, he said.

Read more at Science Daily

Researchers Coax Clays to Make Human Bone

Weak bones, broken bones, damaged bones, arthritic bones. Whether damaged by injury, disease or age, your adult body can't create entirely new bone, but maybe science can. Researchers at North Dakota State University, Fargo, are making strides in tissue engineering, designing scaffolds that may lead to ways to regenerate bone. Published in the Journal of Biomedical Materials Research Part A, the research of Dr. Kalpana Katti, Dr. Dinesh Katti and graduate student Avinash Ambre includes a novel method that uses nanosized clays to make scaffolds to mineralize bone minerals such as hydroxyapatite.

The NDSU research team's 3-D mesh scaffold is composed of degradable materials that are compatible to human tissue. Over time, the cells generate bone and the scaffold deteriorates. As indicated in the NDSU team's published scientific research from 2008 to 2013, the nanoclays enhance the mechanical properties of the scaffold by enabling scaffold to bear load while bone generates. An interesting finding by the Katti group has shown that the nanoclays also impart useful biological properties to the scaffold.

"The biomineralized nanoclays also impart osteogenic or bone-forming abilities to the scaffold to enable birth of bone," said Dr. Kalpana Katti, Distinguished Professor of civil engineering at NDSU. "Although it would have been exciting to say that this finding had a 'Eureka moment,' this discovery was a methodical exploration of simulations and modeling, indicating that amino acid modified nanoclays are viable new nanomaterials," said Katti. The work was initially published in the Journal of Biomacromolecules in 2005. The current findings point toward the potential use of nanoclays for broader applications in medicine.

The NDSU's group most recent study in the Journal of Biomedical Materials Research Part A, published online Feb. 15, 2013, reports that nanoclays mediate human mesenchymal stem cell differentiation into bone cells and grow bone. The Katti research group uses amino acids, the building blocks of life, to modify clay structures and the modified nanoclays coax new bone growth. "Our current research studies underway involve the use of bioreactors that mimic fluid/blood flow in the human body during bone tissue regeneration," said Dr. Kalpana Katti.

The Katti group at NDSU has pioneered the use of nanoclays in bone regeneration since 2008, with research results appearing in Biomedical Materials, ASME Journal of Nanotechnology for Engineering and Medicine, Materials Science and Engineering C, along with the February 2013 publication in the Journal of Biomedical Materials Research Part A.

Read more at Science Daily

Science vs. Fiction: 'After Earth'

What happens if the planet turns on us?

The sci-fi adventure film "After Earth," a kind of family affair starring Will Smith and his son Jaden Smith, is really two movies in one. The film's bookend segments are set aboard interstellar spacecraft with high-tech gadgetry, a thousand or so years into the future.

But the film's middle passages involve conjecture on biology, ecology and a particularly intriguing premise: What would happen if the Earth, as an organism, evolved to defend itself against the harmful human species? We take a look at the film's blend of biological and technological fiction to see if there's any basis in reality.

Predatory plants

Fiction: In several early scenes, Kitai is seen running through beautiful but deadly forest glades in which predatory plants appear to have limited movement and even locomotion.

Science: There are more than 400 known species of carnivorous plants -- or more accurately, insectovorous plants -- which consume their prey through a chemical process similar to digestion. All plants move, of course, but usually too slowly to be discerned without the help of time-lapse photography. But there are exceptions: Several underwater plant species move about visibly, in still water, and the famous Venus fly trap snaps shut in less than half a second when capturing its prey.
Columbia Pictures


Oxygen boost inhalers

Fiction: In the film, Kitai discovers that the Earth's atmosphere has adapted in at least one specific way to discourage human habitation -- there's not enough oxygen to survive. So he must use a futuristic inhaler which, his father explains, will coat his lungs and boost oxygen absorption.

Science: Modern asthma inhalers don't technically increase oxygen absorption into the bloodstream, but they do facilitate lung function by way of two main types of aerosolized medication: Bronchodilators relax muscle constriction, and anti-inflammatory agents suppress

Read more at Discovery News

Visiting Asteroid Has a Moon

A large asteroid that will sail relatively close past Earth on Friday is not alone. Radar images taken by astronomers on Wednesday revealed the asteroid, known as 1998 QE2, is accompanied by an orbiting moon.

“It was quite a surprise,” Marina Brozovic, a radar scientist with NASA’s Jet Propulsion Laboratory in Pasadena, Calif., said during an NASA interview.

“This is something we did not expect,” she said.

The pair will come as close as about 3.6 million miles to Earth at 4:59 p.m. EDT on Friday. That’s just 15 times farther away than Earth’s moon.

“For an asteroid of this size, it’s a close shave,” said Paul Chodas with NASA’s Near Earth Object program office at JPL.

Measuring about 1.7 miles in diameter, 1998 QE2 is among the largest asteroids with orbits that can pass near Earth.

At its most distant, 1998 QE2 flies to  the far edge of the Main Asteroid Belt, nearly to Jupiter. Its pass on Friday is expected to be its closest approach to Earth for at least the next 200 years.

“For the foreseeable future, there’s nothing to worry about,” Chodas said.

Asteroid 1998 QE2 was not named after the United Kingdom’s Queen Elizabeth II, or the QE2 cruise ship. The designation stems from the date and place of its discovery –  1998 by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research (LINEAR) program.

Astronomers are hoping to get images and data during the flyby that rival what a visiting spacecraft could collect.

From Discovery News

How Turtles Got Their Shells

Turtle shells, which turn out to be complex structures made up of 50 bones, evolved long before dinosaurs roamed the earth, according to new research.

Turtles and their shells now predate the Jurassic period, according to a study in the latest issue of Current Biology. It’s a body design that was built to last, representing millions of years of fine-tuning.

Turtle shells began their transformation more than 260 million years ago in the Permian period, said Tyler Lyson, of Yale University and the Smithsonian, in a press release. “Like other complex structures, the shell evolved over millions of years and was gradually modified into its present-day shape.”

The shell looks like just one solid shield, but because it’s made up of multiple bones, it is formed through the fusion of the turtle’s ribs and vertebrae.

“The reason, I think, that more animals don’t form a shell via the broadening and eventually suturing together of the ribs is that the ribs of mammals and lizards are used to help ventilate the lungs,” Lyson said. “If you incorporate your ribs into a protective shell, then you have to find a new way to breathe!”

He explained that turtles have done just that, with the help of a muscular sling.

That  system evolved in relatives of the turtle such as Eunotosaurus. Discovery of a well-preserved fossil of this extinct South African reptile allowed Lyson and his team to fill a 55-million-year-old gap in the turtle fossil record, showing how the shell formed.

Before the find, the world’s oldest known turtle ancestor was Odontochelys semitestacea, a reptile about 220 million years old. It had a fully developed plastron – the belly side of the shell — but only a partial carapace on its back.

Like turtles, Eunotosaurus had nine broadened ribs and lacked intercostal muscles that run between ribs in certain other animals.

Read more at Discovery News

Ancient Egyptians Crafted Jewelry From Meteorites

An ancient Egyptian iron bead found inside a 5,000-year-old tomb was crafted from a meteorite, new research shows.

The tube-shaped piece of jewelry was first discovered in 1911 at the Gerzeh cemetery, roughly 40 miles (70 kilometers) south of Cairo. Dating between 3350 B.C. and 3600 B.C., beads found at the burial site represent the first known examples of iron use in ancient Egypt, thousands of years before Egypt's Iron Age. And their cosmic origins were suspected from the start.

Soon after the beads were discovered, researchers showed that the metal jewelry was rich in nickel, a signature of iron meteorites. But in the 1980s, academics cast doubt on the beads' celestial source, arguing that the high nickel content could have been the result of smelting.

Scientists from the Open University and the University of Manchester recently analyzed one of the beads with an electron microscope and an X-ray CT scanner. They say the nickel-rich chemical composition of the bead's original metal confirms its meteorite origins.

What's more, the researchers say the bead had a Widmanstätten pattern, a distinctive crystal structure found only in meteorites that cooled at an extremely slow rate inside asteroids when the solar system was forming, according to Nature. Further investigation also showed that the bead was not molded under heat, but rather hammered into shape by cold-working.

The first record of iron smelting in ancient Egypt comes from the sixth century B.C., and iron artifacts from before that time are quite rare, Nature reported.

"Today, we see iron first and foremost as a practical, rather dull metal," study researcher Joyce Tyldesley, an Egyptologist at the University of Manchester, said in a statement. "To the ancient Egyptians, however, it was a rare and beautiful material which, as it fell from the sky, surely had some magical/religious properties."

The iron beads' inclusion in burials also suggests this material was deeply important to ancient Egyptians, Tyldesley added.

Read more at Discovery News

Volcanic Bulges Seen With Microwaves

Don’t try this at home. Your microwave oven uses shorter waves than the L-band microwaves that last March scanned the deadly Galeras volcano in Columbia in the greener image above. The other image is in visible light (on a rare clear day in this area). The microwaves are being used by researchers at NASA to study the land surface, among other things, which is particularly useful when you are dealing with an active volcano, like Galeras, which has a recent history of eruptions and is currently at alert level III. In the last two weeks low level seismicity has accompanied small ash and gas plumes rising from the crater.

L-band microwaves are like those used by a car’s GPS receiver. They can be used to penetrate forest canopies to measure the ground below. So rain or shine, forest or no, detecting even the small changes in the land surface can be done by taking a series of microwave images to see if there is any bulging ground, which is caused by magma rising from below. Such bulges can signal a coming eruption, and so detecting them early is a valuable tool for warning people and saving lives.

The Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) captured the data for the green, false-color microwave image on March 13, 2013, while on board a NASA Gulfstream C-20A aircraft. UAVSAR has a spatial resolution of 6 meters (20 feet) per pixel.

The natural color image was made in 2002 by the Enhanced Thematic Mapper Plus on the Landsat 7 satellite. Landsat 7′s resolution is 30 meters per pixel.

From Discovery News

Is Mars Infested With Pareidolia Rats?

It has finally happened. Not content with (potentially) infecting the pristine Martian surface with our germs, it appears that we’ve sent a rat (yes, a whole rat) to the Red Planet. And this isn’t some far-fetched hypothesis, there’s photographic evidence!

NASA’s Mars rover Curiosity snapped this panorama (above) of the “Rocknest” site with its MastCam camera on sol 52 (Sept. 28, 2012) of the mission. Now, with a keen eye and fertile imagination, a UFO enthusiast realized there was a camouflaged rodent hiding in the rocks. Needless to say, there’s no other evidence supporting this claim, it’s just something that looks like a rodent.

But as you may have guessed, after exercising an ounce of logical thought, what was once a cute furry four-legged creature suddenly becomes… wait for it… this is a good one… a rock. And there you have it ladies and gentlemen: We’ve found a rock on Mars… that looks like a rat.

This certainly isn’t the first time shapes on Mars have fooled the brains of many. What’s more, there’s a name for this psychological phenomenon: pareidolia — possibly an evolutionary trait.

This psychological oddity makes us see familiar objects in apparently random shapes, such as Mars yetis, faces, elephants, black ops bases and parrots on Mars. Pareidolia is the same thing that makes us see the face of Jesus Christ in burnt toast and bunnies in clouds.

Perhaps it’s time to engage some upper-level reasoning and realize that just because there’s a rock on Mars that looks like a rat (whether its a trick of the light, or if it’s genuinely shaped like a small mammal), it doesn’t mean that it is a rat. There is also the possibility that the whole “Mars rat” thing isn’t serious at all and judging by the way the initial report is worded, it could go either way.

Regardless, the story is now in the mainstream and it’s highly likely that our Mars rat will soon get his own Twitter account. Therefore, it’s worth reminding the world that Mars cannot support complex biology like rodents and it’s highly unlikely that any basic lifeforms can be found on the Red Planet’s barren surface today (although there may be some pockets of modern day habitability below the surface).

Read more at Discovery News