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  • richardmitnick 1:06 pm on January 8, 2017 Permalink | Reply
    Tags: 3-D forms, , MIT News, Researchers design one of the strongest lightest materials known   

    From MIT: “Researchers design one of the strongest, lightest materials known” 

    MIT News
    MIT News
    MIT Widget

    January 6, 2017
    David L. Chandler

    This illustration shows the simulation results of tensile and compression tests on 3-D graphene. Image: Zhao Qin

    Porous, 3-D forms of graphene developed at MIT can be 10 times as strong as steel but much lighter.

    Access mp4 video here .
    A team of MIT engineers has successfully designed a new 3-D material with five percent the density of steel and ten times the strength, making it one of the strongest, lightweight materials known.
    Video: Melanie Gonick/MIT

    A team of researchers at MIT has designed one of the strongest lightweight materials known, by compressing and fusing flakes of graphene, a two-dimensional form of carbon. The new material, a sponge-like configuration with a density of just 5 percent, can have a strength 10 times that of steel.

    In its two-dimensional form, graphene is thought to be the strongest of all known materials. But researchers until now have had a hard time translating that two-dimensional strength into useful three-dimensional materials.

    The new findings show that the crucial aspect of the new 3-D forms has more to do with their unusual geometrical configuration than with the material itself, which suggests that similar strong, lightweight materials could be made from a variety of materials by creating similar geometric features.

    The findings are being reported today in the journal Science Advances, in a paper by Markus Buehler, the head of MIT’s Department of Civil and Environmental Engineering (CEE) and the McAfee Professor of Engineering; Zhao Qin, a CEE research scientist; Gang Seob Jung, a graduate student; and Min Jeong Kang MEng ’16, a recent graduate.Other groups had suggested the possibility of such lightweight structures, but lab experiments so far had failed to match predictions, with some results exhibiting several orders of magnitude less strength than expected. The MIT team decided to solve the mystery by analyzing the material’s behavior down to the level of individual atoms within the structure. They were able to produce a mathematical framework that very closely matches experimental observations.

    Two-dimensional materials — basically flat sheets that are just one atom in thickness but can be indefinitely large in the other dimensions — have exceptional strength as well as unique electrical properties. But because of their extraordinary thinness, “they are not very useful for making 3-D materials that could be used in vehicles, buildings, or devices,” Buehler says. “What we’ve done is to realize the wish of translating these 2-D materials into three-dimensional structures.”

    The team was able to compress small flakes of graphene using a combination of heat and pressure. This process produced a strong, stable structure whose form resembles that of some corals and microscopic creatures called diatoms. These shapes, which have an enormous surface area in proportion to their volume, proved to be remarkably strong. “Once we created these 3-D structures, we wanted to see what’s the limit — what’s the strongest possible material we can produce,” says Qin. To do that, they created a variety of 3-D models and then subjected them to various tests. In computational simulations, which mimic the loading conditions in the tensile and compression tests performed in a tensile loading machine, “one of our samples has 5 percent the density of steel, but 10 times the strength,” Qin says.

    Buehler says that what happens to their 3-D graphene material, which is composed of curved surfaces under deformation, resembles what would happen with sheets of paper. Paper has little strength along its length and width, and can be easily crumpled up. But when made into certain shapes, for example rolled into a tube, suddenly the strength along the length of the tube is much greater and can support substantial weight. Similarly, the geometric arrangement of the graphene flakes after treatment naturally forms a very strong configuration.

    The new configurations have been made in the lab using a high-resolution, multimaterial 3-D printer. They were mechanically tested for their tensile and compressive properties, and their mechanical response under loading was simulated using the team’s theoretical models. The results from the experiments and simulations matched accurately.

    The new, more accurate results, based on atomistic computational modeling by the MIT team, ruled out a possibility proposed previously by other teams: that it might be possible to make 3-D graphene structures so lightweight that they would actually be lighter than air, and could be used as a durable replacement for helium in balloons. The current work shows, however, that at such low densities, the material would not have sufficient strength and would collapse from the surrounding air pressure.

    But many other possible applications of the material could eventually be feasible, the researchers say, for uses that require a combination of extreme strength and light weight. “You could either use the real graphene material or use the geometry we discovered with other materials, like polymers or metals,” Buehler says, to gain similar advantages of strength combined with advantages in cost, processing methods, or other material properties (such as transparency or electrical conductivity).

    “You can replace the material itself with anything,” Buehler says. “The geometry is the dominant factor. It’s something that has the potential to transfer to many things.”

    The unusual geometric shapes that graphene naturally forms under heat and pressure look something like a Nerf ball — round, but full of holes. These shapes, known as gyroids, are so complex that “actually making them using conventional manufacturing methods is probably impossible,” Buehler says. The team used 3-D-printed models of the structure, enlarged to thousands of times their natural size, for testing purposes.

    For actual synthesis, the researchers say, one possibility is to use the polymer or metal particles as templates, coat them with graphene by chemical vapor deposit before heat and pressure treatments, and then chemically or physically remove the polymer or metal phases to leave 3-D graphene in the gyroid form. For this, the computational model given in the current study provides a guideline to evaluate the mechanical quality of the synthesis output.

    The same geometry could even be applied to large-scale structural materials, they suggest. For example, concrete for a structure such a bridge might be made with this porous geometry, providing comparable strength with a fraction of the weight. This approach would have the additional benefit of providing good insulation because of the large amount of enclosed airspace within it.

    Because the shape is riddled with very tiny pore spaces, the material might also find application in some filtration systems, for either water or chemical processing. The mathematical descriptions derived by this group could facilitate the development of a variety of applications, the researchers say.

    “This is an inspiring study on the mechanics of 3-D graphene assembly,” says Huajian Gao, a professor of engineering at Brown University, who was not involved in this work. “The combination of computational modeling with 3-D-printing-based experiments used in this paper is a powerful new approach in engineering research. It is impressive to see the scaling laws initially derived from nanoscale simulations resurface in macroscale experiments under the help of 3-D printing,” he says.

    This work, Gao says, “shows a promising direction of bringing the strength of 2-D materials and the power of material architecture design together.”

    The research was supported by the Office of Naval Research, the Department of Defense Multidisciplinary University Research Initiative, and BASF-North American Center for Research on Advanced Materials.

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  • richardmitnick 8:03 am on August 7, 2015 Permalink | Reply
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    From MIT: “How chronic inflammation can lead to cancer” 

    MIT News

    August 7, 2015
    Helen Knight, MIT News correspondent

    Bogdan Fedeles (right), a research associate in the MIT Department of Biological Engineering and lead author on a new paper on the link between chronic inflammation and cancer, examines a DNA model with professor John Essigmann, who led the current research. Photo: Jose-Luis Olivares/MIT

    Researchers have uncovered a way chronic inflammation can lead to cancer. Panel 1 shows a normal DNA base pair of cytosine (C) and guanine (G). In panel 2, inflammation, represented by a red background, damages the base pair. A chlorine atom (Cl) is added to the cytosine, resulting in a cytosine lesion called 5-chlorocytosine. In panel 3, the cytosine lesion is now able to base pair with adenine (A). In panel 4, the adenine directs incorporation of an opposing thymine (T) at the position of the initial (C). Thus, the formation of 5-chlorocytosine in DNA drives the formation of C:G-to-T:A mutations. Image: Jose-Luis Olivares/MIT

    Bogdan Fedeles holds up a model of 5-chlorocytosine, a mutagenic DNA lesion occurring in inflamed tissues that may explain the link between chronic inflammation and cancer. Photo: Jose-Luis Olivares/MIT

    Researchers discover how the immune system can create cancerous DNA mutations when fighting off infection.

    Chronic inflammation caused by disease or exposure to dangerous chemicals has long been linked to cancer, but exactly how this process takes place has remained unclear.

    Now, a precise mechanism by which chronic inflammation can lead to cancer has been uncovered by researchers at MIT — a development that could lead to improved targets for preventing future tumors.

    In a paper published this week in the Proceedings of the National Academy of Sciences, the researchers unveil how one of a battery of chemical warfare agents used by the immune system to fight off infection can itself create DNA mutations that lead to cancer.

    As many as one in five cancers are believed to be caused or promoted by inflammation. These include mesothelioma, a type of lung cancer caused by inflammation following chronic exposure to asbestos, and colon cancer in people with a history of inflammatory bowel disease, says Bogdan Fedeles, a research associate in the Department of Biological Engineering at MIT, and the paper’s lead author.

    Innate immune response

    Inflammation is part of the body’s innate response to invading pathogens or potentially harmful irritants. The immune system attacks the invader with a number of reactive molecules designed to neutralize it, including hydrogen peroxide, nitric oxide and hypochlorous acid.

    However, these molecules can also cause collateral damage to healthy tissue around the infection site: “The presence of a foreign pathogen activates the immune response, which tries to fight off the bacteria, but in this process it also damages some of the normal cells,” Fedeles explains.

    Previous work by Peter Dedon, Steven Tannenbaum, Gerald Wogan, and James Fox — all professors of biological engineering at MIT — had identified the presence of a lesion, or site of damage in the structure of DNA, called 5-chlorocytosine (5ClC) in the inflamed tissues of mice infected with the pathogen Helicobacter hepaticus. This lesion, a damaged form of the normal DNA base cytosine, is caused by the reactive molecule hypochlorous acid — the main ingredient in household bleach — which is generated by the immune system.

    The lesion, 5ClC, was present in remarkably high levels within the tissue, says John Essigmann, the William R. (1956) and Betsy P. Leitch Professor in Residence Professor of Chemistry, Toxicology and Biological Engineering at MIT, who led the current research.

    “They found the lesions were very persistent in DNA, meaning we don’t have a repair system to take them out,” Essigmann says. “In our field lesions that are persistent, if they are also mutagenic, are the kind of lesions that would initiate cancer,” he adds.

    DNA sequencing of a developing gastrointestinal tumor revealed two types of mutation: cytosine (C) bases changing to thymine (T) bases, and adenine (A) bases changing to guanine (G) bases. Since 5ClC had not yet been studied as a potentially carcinogenic mutagen, the researchers decided to investigate the lesion further, in a bid to uncover if it is indeed mutagenic.

    Using a technique previously developed in Essigmann’s laboratory, the researchers first placed the 5ClC lesion at a specific site within the genome of a bacterial virus. They then replicated the virus within the cell.

    The researchers found that, rather than always pairing with a guanine base as a cytosine would, the 5ClC instead paired with an adenine base around 5 percent of the time — a medically relevant mutation frequency, according to Essigmann.

    Damaged DNA

    The findings suggest that the immune system, when triggered by infection, fires hypochlorous acid at the site, damaging cytosines in the DNA of the surrounding healthy tissue. This damage causes some of the cytosines to become 5ClC.

    In addition, the researchers hypothesize that the hypochlorous acid also damages cytosines in the nucleotide pool, which cells use as the reservoir of nucleotides that will become part of the DNA of replicating cells, Essigmann says. “So 5ClC forms first in genomic DNA, and secondly it can form in the nucleotide pool, meaning the nucleotides in the pool are mutagenic in themselves,” he explains. “This scenario would best explain the work of James Fox and his MIT colleagues on gastrointestinal cancer.”

    To confirm that 5ClC is mutagenic in human DNA, the researchers replicated the genome containing the lesion with a variety of different types of polymerase, the enzyme that assembles DNA, including human polymerases. “In all cases we found that 5ClC is mutagenic, and causes the same kind of mutations seen within cells,” Fedeles says. “That gave us confidence that this phenomenon would in fact happen in human cells containing high levels of 5ClC.”

    What’s more, the C-to-T mutation characteristic of 5ClC is extremely common, and is present in more than 50 percent of mutagenic “signatures,” or patterns of DNA mutations, associated with cancerous tumors. “We believe that in the context of inflammation-induced damage of DNA, many of these C-to-T mutations may be caused by 5ClC, possibly in correlation with other types of mutations as part of these mutational signatures,” Fedeles says.

    Yinsheng Wang, a principal investigator in the Department of Chemistry at the University of California at Riverside who was not involved in the research, says the paper provides a novel mechanistic link between chronic inflammation and cancer development. “With a combination of biochemical, genetic, and structural biology approaches, the researchers have found that 5-chlorocytosine is intrinsically miscoding during DNA replication and it could give rise to significant frequencies of C-to-T mutation, a type of mutation that is frequently observed in human cancers,” Wang says.

    Studies of tissue samples of patients suffering from inflammatory bowel disease have found significant levels of 5ClC, Fedeles adds. By comparing these levels with his team’s findings on how mutagenic 5ClC is, the researchers predict that accumulation of the lesions would increase the mutation rate of a cell up to 30-fold, says Fedeles, who was honored with the prestigious Benjamin F. Trump award at the 2015 Aspen Cancer Conference for the research.

    The researchers now plan to carry out further studies to confirm their prediction, Fedeles says.

    See the full article here.

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  • richardmitnick 8:56 am on July 23, 2015 Permalink | Reply
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    From MIT: “New technique allows analysis of clouds around exoplanets” 

    MIT News

    March 3, 2015
    Helen Knight

    Team describes use of method to determine properties of clouds surrounding the exoplanet Kepler-7b.

    Analysis of data from the Kepler space telescope has shown that roughly half of the dayside of the exoplanet Kepler-7b is covered by a large cloud mass. Statistical comparison of more than 1,000 atmospheric models show that these clouds are most likely made of Enstatite, a common Earth mineral that is in vapor form at the extreme temperature on Kepler-7b. These models varied the altitude, condensation, particle size, and chemical composition of the clouds to find the right reflectivity and color properties to match the observed signal from the exoplanet. Courtesy of NASA (edited by Jose-Luis Olivares/MIT)

    Meteorologists sometimes struggle to accurately predict the weather here on Earth, but now we can find out how cloudy it is on planets outside our solar system, thanks to researchers at MIT.

    In a paper to be published in the Astrophysical Journal, researchers in the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at MIT describe a technique that analyzes data from NASA’s Kepler space observatory to determine the types of clouds on planets that orbit other stars, known as exoplanets.

    NASA Kepler Telescope

    The team, led by Kerri Cahoy, an assistant professor of aeronautics and astronautics at MIT, has already used the method to determine the properties of clouds on the exoplanet Kepler-7b. The planet is known as a “hot Jupiter,” as temperatures in its atmosphere hover at around 1,700 kelvins.

    NASA’s Kepler spacecraft was designed to search for Earth-like planets orbiting other stars. It was pointed at a fixed patch of space, constantly monitoring the brightness of 145,000 stars. An orbiting exoplanet crossing in front of one of these stars causes a temporary dimming of this brightness, allowing researchers to detect its presence.

    Researchers have previously shown that by studying the variations in the amount of light coming from these star systems as a planet transits, or crosses in front or behind them, they can detect the presence of clouds in that planet’s atmosphere. That is because particles within the clouds will scatter different wavelengths of light.

    Modeling cloud formation

    To find out if this data could be used to determine the composition of these clouds, the MIT researchers studied the light signal from Kepler-7b. They used models of the temperature and pressure of the planet’s atmosphere to determine how different types of clouds would form within it, says lead author Matthew Webber, a graduate student in Cahoy’s group at MIT.

    “We then used those cloud models to determine how light would reflect off the atmosphere of the planet [for each type of cloud], and tried to match these possibilities to the actual observations from the Kepler mission itself,” Webber says. “So we ran a large set of models, to see which models fit best statistically to the observations.”

    By working backward in this way, they were able to match the Kepler spacecraft data to a type of cloud made out of vaporized silicates and magnesium. The extremely high temperatures in the Kepler-7b atmosphere mean that some minerals that commonly exist as rocks on Earth’s surface instead exist as vapors high up in the planet’s atmosphere. These mineral vapors form small cloud particles as they cool and condense.

    Kepler-7b is a tidally locked planet, meaning it always shows the same face to its star — just as the moon does to Earth. As a result, around half of the planet’s day side — that which constantly faces the star — is covered by these magnesium silicate clouds, the team found.

    “We are really doing nothing more complicated than putting a telescope into space and staring at a star with a camera,” Cahoy says. “Then we can use what we know about the universe, in terms of temperatures and pressures, how things mix, how they stratify in an atmosphere, to try to figure out what mix of things would be causing the observations that we’re seeing from these very basic instruments,” she says.

    A clue on exoplanet atmospheres

    Understanding the properties of the clouds on Kepler-7b, such as their mineral composition and average particle size, tells us a lot about the underlying physical nature of the planet’s atmosphere, says team member Nikole Lewis, a postdoc in EAPS. What’s more, the method could be used to study the properties of clouds on different types of planet, Lewis says: “It’s one of the few methods out there that can help you determine if a planet even has an atmosphere, for example.”

    A planet’s cloud coverage and composition also has a significant impact on how much of the energy from its star it will reflect, which in turn affects its climate and ultimately its habitability, Lewis says. “So right now we are looking at these big gas-giant planets because they give us a stronger signal,” she says. “But the same methodology could be applied to smaller planets, to help us determine if a planet is habitable or not.”

    The researchers hope to use the method to analyze data from NASA’s follow-up to the Kepler mission, known as K2, which began studying different patches of space last June. They also hope to use it on data from MIT’s planned Transiting Exoplanet Survey Satellite (TESS) mission, says Cahoy.


    “TESS is the follow-up to Kepler, led by principal investigator George Ricker, a senior research scientist in the MIT Kavli Institute for Astrophysics and Space Research. It will essentially be taking similar measurements to Kepler, but of different types of stars,” Cahoy says. “Kepler was tasked with staring at one group of stars, but there are a lot of stars, and TESS is going to be sampling the brightest stars across the whole sky,” she says.

    This paper is the first to take circulation models including clouds and compare them with the observed distribution of clouds on Kepler-7b, says Heather Knutson, an assistant professor of planetary science at Caltech who was not involved in the research.

    “Their models indicate that the clouds on this planet are most likely made from liquid rock,” Knutson says. “This may sound exotic, but this planet is a roasting hot gas-giant planet orbiting very close to its host star, and we should expect that it might look quite different than our own Jupiter.”

    See the full article here.

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  • richardmitnick 1:54 pm on July 16, 2015 Permalink | Reply
    Tags: , MIT News, , Weyl Points   

    From MIT: “Long-sought phenomenon finally detected” 

    MIT News

    July 16, 2015
    David L. Chandler | MIT News Office

    The gyroid surface with a dime on top. Image: Ling Lu and Qinghui Yan

    Weyl points, first predicted in 1929, observed for the first time.

    Part of a 1929 prediction by physicist Hermann Weyl — of a kind of massless particle that features a singular point in its energy spectrum called the “Weyl point” — has finally been confirmed by direct observation for the first time, says an international team of physicists led by researchers at MIT. The finding could lead to new kinds of high-power single-mode lasers and other optical devices, the team says.

    For decades, physicists thought that the subatomic particles called neutrinos were, in fact, the massless particles that Weyl had predicted — a possibility that was ultimately eliminated by the 1998 discovery that neutrinos do have a small mass. While thousands of scientific papers have been written about the theoretical particles, until this year there had seemed little hope of actually confirming their existence.

    “Every single paper written about Weyl points was theoretical, until now,” says Marin Soljačić, a professor of physics at MIT and the senior author of a paper published this week in the journal Science confirming the detection. (Another team of researchers at Princeton University and elsewhere independently made a different detection of Weyl particles; their paper appears in the same issue of Science).

    Ling Lu, a research scientist at MIT and lead author of that team’s paper, says the elusive points can be thought of as equivalent to theoretical entities known as magnetic monopoles. These do not exist in the real world: They would be the equivalent of cutting a bar magnet in half and ending up with separate north and south magnets, whereas what really happens is you end up with two shorter magnets, each with two poles. But physicists often carry out their calculations in terms of momentum space (also called reciprocal space) rather than ordinary three-dimensional space, Lu explains, and in that framework magnetic monopoles can exist — and their properties match those of Weyl points.

    The achievement was made possible by a novel use of a material called a photonic crystal. In this case, Lu was able to calculate precise measurements for the construction of a photonic crystal predicted to produce the manifestation of Weyl points — with dimensions and precise angles between arrays of holes drilled through the material, a configuration known as a gyroid structure. This prediction was then proved correct by a variety of sophisticated measurements that exactly matched the characteristics expected for such points.

    Some kinds of gyroid structures exist in nature, Lu points out, such as in certain butterfly wings. In such natural occurrences, gyroids are self-assembled, and their structure was already known and understood.

    Two years ago, researchers had predicted that by breaking the symmetries in a kind of mathematical surfaces called “gyroids” in a certain way, it might be possible to generate Weyl points — but realizing that prediction required the team to calculate and build their own materials. In order to make these easier to work with, the crystal was designed to operate at microwave frequencies, but the same principles could be used to make a device that would work with visible light, Lu says. “We know a few groups that are trying to do that,” he says.

    A number of applications could take advantage of these new findings, Soljačić says. For example, photonic crystals based on this design could be used to make large-volume single-mode laser devices. Usually, Soljačić says, when you scale up a laser, there are many more modes for the light to follow, making it increasingly difficult to isolate the single desired mode for the laser beam, and drastically limiting the quality of the laser beam that can be delivered.

    But with the new system, “No matter how much you scale it up, there are very few possible modes,” he says. “You can scale it up as large as you want, in three dimensions, unlike other optical systems.”

    That issue of scalability in optical systems is “quite fundamental,” Lu says; this new approach offers a way to circumvent it. “We have other applications in mind,” he says, to take advantage of the device’s “optical selectivity in a 3-D bulk object.” For example, a block of material could allow only one precise angle and color of light to pass through, while all others would be blocked.

    “This is an interesting development, not just because Weyl points have been experimentally observed, but also because they endow the photonics crystals which realize them with unique optical properties,” says Ashvin Vishwanath, a professor of physics at the University of California at Berkeley who was not involved in this research. “Professor Soljačić’s group has a track record of rapidly converting new science into creative devices with industry applications, and I am looking forward to seeing how Weyl photonics crystals evolve.”

    Besides Lu and Soljačić, the team included Zhiyu Wang, Dexin Ye, and Lixin Ran of Zhejiang University in China and, at MIT, assistant professor of physics Liang Fu and John Joannopoulos, the Francis Wright Davis Professor of Physics and director of the Institute for Soldier Nanotechnologies (ISN). The work was supported by the U.S. Army through the ISN, the Department of Energy, the National Science Foundation, and the Chinese National Science Foundation.

    See the full article here.
    The Princeton University article is here.

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  • richardmitnick 10:03 am on June 16, 2015 Permalink | Reply
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    From MIT: “Small thunderstorms may add up to massive cyclones on Saturn” 

    MIT News

    June 15, 2015
    Jennifer Chu | MIT News Office

    Saturn’s north polar vortex.m Image courtesy of Caltech/Space Science Institute

    New model may predict cyclone activity on other planets.

    For the last decade, astronomers have observed curious “hotspots” on Saturn’s poles. In 2008, NASA’s Cassini spacecraft beamed back close-up images of these hotspots, revealing them to be immense cyclones, each as wide as the Earth.

    NASA Cassini Spacecraft

    Scientists estimate that Saturn’s cyclones may whip up 300 mph winds, and likely have been churning for years.

    While cyclones on Earth are fueled by the heat and moisture of the oceans, no such bodies of water exist on Saturn. What, then, could be causing such powerful, long-lasting storms?

    In a paper published today in the journal Nature Geoscience, atmospheric scientists at MIT propose a possible mechanism for Saturn’s polar cyclones: Over time, small, short-lived thunderstorms across the planet may build up angular momentum, or spin, within the atmosphere — ultimately stirring up a massive and long-lasting vortex at the poles.

    The researchers developed a simple model of Saturn’s atmosphere, and simulated the effect of multiple small thunderstorms forming across the planet over time. Eventually, they observed that each thunderstorm essentially pulls air towards the poles — and together, these many small, isolated thunderstorms can accumulate enough atmospheric energy at the poles to generate a much larger and long-lived cyclone.

    The team found that whether a cyclone develops depends on two parameters: the size of the planet relative to the size of an average thunderstorm on it, and how much storm-induced energy is in its atmosphere. Given these two parameters, the researchers predicted that Neptune, which bears similar polar hotspots, should generate transient polar cyclones that come and go, while Jupiter should have none.

    Morgan O’Neill, the paper’s lead author and a former PhD student in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), says the team’s model may eventually be used to gauge atmospheric conditions on planets outside the solar system. For instance, if scientists detect a cyclone-like hotspot on a far-off exoplanet, they may be able to estimate storm activity and general atmospheric conditions across the entire planet.

    “Before it was observed, we never considered the possibility of a cyclone on a pole,” says O’Neill, who is now a postdoc at the Weizmann Institute of Science in Israel.

    “Only recently did Cassini give us this huge wealth of observations that made it possible, and only recently have we had to think about why [polar cyclones] occur.”

    O’Neill’s co-authors are Kerry Emanuel, the Cecil and Ida Green Professor of Earth, Atmospheric and Planetary Sciences, and Glenn Flierl, a professor of oceanography in EAPS.

    Beta-drifting toward a cyclone

    Polar cyclones on Saturn are a puzzling phenomenon, since the planet, known as a gas giant, lacks an essential ingredient for brewing up such storms: water on its surface.

    “There’s no surface at all — it just gets denser as you get deeper,” O’Neill says. “If you lack choppy waters or a frictional surface that allows wind to converge, which is how hurricanes form on Earth, how can you possibly get something that looks similar on a gas giant?”

    The answer, she found, may be something called “beta drift” — a phenomenon by which a planet’s spin causes small thunderstorms to drift toward the poles. Beta drift drives the motion of hurricanes on Earth, without requiring the presence of water. When a storm forms, it spins in one direction at the surface, and the opposite direction toward the upper atmosphere, creating a “dipole of vorticity.” (In fact, videos of hurricanes taken from space actually depict the storm’s spin as opposite to what’s observed on the ground.)

    “The whole atmosphere is kind of being dragged by the planet as the planet rotates, so all this air has some ambient angular momentum,” O’Neill explains. “If you converge a bunch of that air at the base of a thunderstorm, you’re going to get a small cyclone.”

    The combination of a planet’s rotation and a circulating storm generates secondary features called beta gyres that wrap around a storm and essentially split its dipole in half, tugging the top half toward the equator, and the bottom half toward the pole.

    The team developed a model of Saturn’s atmosphere and ran hundreds of simulations for hundreds of days each, allowing small thunderstorms to pop up across the planet. The researchers observed that multiple thunderstorms experienced beta drift over time, and eventually accumulated enough atmospheric circulation to create a much larger cyclone at the poles.

    “Each of these storms is beta-drifting a little bit before they sputter out and die,” O’Neill says. “This mechanism means that little thunderstorms — fast, abundant, but not very strong thunderstorms — over a long period of time can actually accumulate so much angular momentum right on the pole, that you get a permanent, wildly strong cyclone.”

    Next stop: Jupiter

    The team also explored conditions in which planets would not form polar cyclones, even though they may experience thunderstorms. The researchers found that whether a polar cyclone forms depends on two parameters: the energy within a planet’s atmosphere, or the total intensity of its thunderstorms; and the average size of its thunderstorms, relative to the size of the planet itself. Specifically, the larger an average thunderstorm compared to a planet’s size, the more likely a polar cyclone is to develop.

    O’Neill applied this relationship to Saturn, Jupiter, and Neptune. In the case of Saturn, the planet’s atmospheric conditions and storm activity are within the range that would generate a large polar cyclone. In contrast, Jupiter is unlikely to host any polar cyclones, as the ratio of any storm to its overall size would be extremely small. The dimensions of Neptune suggest that polar cyclones may exist there, albeit on a fleeting basis.

    “Saturn has an intense cyclone at each pole,” says Andrew Ingersoll, professor of planetary science at Caltech, who was not involved in the study. “The model successfully accounts for that. Jupiter doesn’t seem to have polar cyclones like Saturn’s, but Jupiter isn’t tipped over as much as Saturn, so we don’t get a good view of the poles. Thus the apparent absence of polar cyclones on Jupiter is still a mystery.”

    The researchers are eager to see whether their predictions, particularly for Jupiter, bear out. Next summer, NASA’s Juno spacecraft is scheduled to enter into an orbit around Jupiter, kicking off a one-year mission to map and explore Jupiter’s atmosphere.

    “If what we know about Jupiter currently is correct, we predict that we won’t see these wildly strong cyclones,” O’Neill says. “We’ll find out next year if our predictions are true.”

    This research was funded in part by the National Science Foundation.

    See the full article here.

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  • richardmitnick 9:04 am on May 28, 2015 Permalink | Reply
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    From MIT: “Remote observing now in progress” 

    MIT News

    May 27, 2015
    Helen Hill | EAPS

    Students can now remotely access and program telescopes at MIT’s Wallace Astronomical Observatory in Westford, Massachusetts. Photo: Amanda Bosh

    Students in Building 54 remotely observe the night sky using a telescope at the Wallace Observatory. Photo courtesy of R. Binzel.

    After two years of work, MIT’s Wallace Observatory team has “perfected” the ability to control its fleet of smaller telescopes remotely and automatically.

    Looking up through a telescope at the contours of the moon or at Saturn with its faint yet startlingly familiar ring system can be a life changing experience. But in the age of the Internet, sensors, and the ability to connect to observing equipment across the world from a simple desktop, it was perhaps only a matter of time before the attention of MIT’s Wallace Observatory team would turn to making their suite of off-campus telescopes work remotely.

    MIT Wallace Observatory
    MIT’s Wallace Observatory

    The George R. Wallace Jr. Astrophysical Observatory (WAO), in Westford, Massachusetts, is a teaching and research facility run by the Planetary Astronomy Lab in the MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS). Until now, students in the MIT observing courses 12.409 (Hands-on Astronomy: Observing Stars and Planets) and 12.410 (Observational Techniques of Optical Astronomy), have had to travel the 40 miles to and from Wallace to make their observations. But no more. Two years ago Wallace’s roll-off roof-shed that houses four 14-inch Celestron C14 telescopes was retrofitted with a custom system that allows it to be operated and scripted by a standard astronomy equipment language — and can stow the telescopes safely if bad weather arrives.

    One of the greatest barriers to student data in the classes had been the two-hour round-trip transit time to WAO. Between getting there and getting back, an observing evening became such an investment of time that instructors needed to be very careful about deciding which nights to go, and which to let pass because they didn’t look like they were going to be quite good enough. With the new system based in the Green Building (Building 54), students can get started almost immediately when they and their telescopes are available — and if it should suddenly cloud up, they can close down and walk back to their dorms with only half an hour lost.

    “After working on it for the past two years, we’ve at last ‘perfected’ the ability to observe with the C-14s remotely, so that by the end of the fall semester, 12.410 had students using the telescopes on Monday and Wednesday evenings from campus without the need to drive out to Wallace — without anyone being out there at all, actually,” says Michael Person, a research scientist in the Planetary Astronomy Lab and director of the Wallace Observatory.

    The lion’s share of the work was carried out in-house by an assortment of stellar students in the Undergraduate Research Opportunities Programs and others, coordinated by site manager Tim Brothers. Effective and reliable design and installation of the custom shed opening and closing mechanism; acquisition, installation, and testing of remote weather sensors, and nightvision capable video cameras; as well as development of appropriate firewalls to protect the systems in Westford from hackers while allowing control from the designated remote observing lab in Cambridge, all had to come together to make observing direct from Building 54 a reality.

    Brothers, who also fully refurbished the vintage “orange tube” C-14s to their original specifications over this past summer, is pleased with how things are developing. He recently expressed excitement at the fact that continuing developments have allowed the beginning of automated observing — the ability to script observations from start to finish and to “wake up with tons of data waiting for us.” A recent milestone this spring was an entirely scripted observation containing two different data sets — an asteroid light curve and Pluto astrometry — on one telescope, resulting in almost eight hours’ worth of data.

    Meanwhile, automation of the domes housing Wallace’s two largest telescopes — 24-inch and 16-inch Cassegrain reflectors — is still on the WAO’s to-do list. Person says, “My long-term goal is to have the entire site ready for fully remote operations, but having students able to use the shed telescopes remotely is a first big milestone.”

    “We still can’t control the weather,” he adds ruefully, “but maybe someone else in the department is working on that.”

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  • richardmitnick 8:29 am on May 28, 2015 Permalink | Reply
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    From MIT: “Spinning a new version of silk” 

    MIT News

    May 28, 2015
    David L. Chandler | MIT News Office

    Microscope images of lab-produced fibers confirm the results of the MIT researchers’ simulations of spider silk. At top are optical microscope images, and, at bottom, are scanning electron microscope images. At left are fibers 8 micrometers across, and, at right, are thinner, 3 micrometer fibers.
    Courtesy of the researchers

    Molecular-level simulations of different lengths of silk molecules called fibroins, after being exposed to flow to simulate a spider’s spinning process, reveal the key importance of the length of the molecular chains in achieving well-bonded fibers. At left, the fibroins have a length of 4 units, and, at right, 12 units. Below each “snapshot” of the simulation is a diagram showing the connections between units. The longer chains produce a much stronger fiber. Courtesy of the researchers

    After years of research decoding the complex structure and production of spider silk, researchers have now succeeded in producing samples of this exceptionally strong and resilient material in the laboratory. The new development could lead to a variety of biomedical materials — from sutures to scaffolding for organ replacements — made from synthesized silk with properties specifically tuned for their intended uses.

    The findings are published this week in the journal Nature Communications by MIT professor of civil and environmental engineering (CEE) Markus Buehler, postdocs Shangchao Lin and Seunghwa Ryu, and others at MIT, Tufts University, Boston University, and in Germany, Italy, and the U.K.

    The research, which involved a combination of simulations and experiments, paves the way for “creating new fibers with improved characteristics” beyond those of natural silk, says Buehler, who is also the department head in CEE. The work, he says, should make it possible to design fibers with specific characteristics of strength, elasticity, and toughness.

    The new synthetic fibers’ proteins — the basic building blocks of the material — were created by genetically modifying bacteria to make the proteins normally produced by spiders. These proteins were then extruded through microfluidic channels designed to mimic the effect of an organ, called a spinneret, that spiders use to produce natural silk fibers.

    No spiders needed

    While spider silk has long been recognized as among the strongest known materials, spiders cannot practically be bred to produce harvestable fibers — so this new approach to producing a synthetic, yet spider-like, silk could make such strong and flexible fibers available for biomedical applications. By their nature, spider silks are fully biocompatible and can be used in the body without risk of adverse reactions; they are ultimately simply absorbed by the body.

    The researchers’ “spinning” process, in which the constituent proteins dissolved in water are extruded through a tiny opening at a controlled rate, causes the molecules to line up in a way that produces strong fibers. The molecules themselves are a mixture of hydrophobic and hydrophilic compounds, blended so as to naturally align to form fibers much stronger than their constituent parts. “When you spin it, you create very strong bonds in one direction,” Buehler says.

    The team found that getting the blend of proteins right was crucial. “We found out that when there was a high proportion of hydrophobic proteins, it would not spin any fibers, it would just make an ugly mass,” says Ryu, who worked on the project as a postdoc at MIT and is now an assistant professor at the Korea Advanced Institute of Science and Technology. “We had to find the right mix” in order to produce strong fibers, he says.

    Closing the loop

    This project represents the first use of simulations to understand silk production at the molecular level. “Simulation is critical,” Buehler explains: Actually synthesizing a protein can take several months; if that protein doesn’t turn out to have exactly the right properties, the process would have to start all over.

    Using simulations makes it possible to “scan through a large range of proteins until we see changes in the fiber stiffness,” and then home in on those compounds, says Lin, who worked on the project as a postdoc at MIT and is now an assistant professor at Florida State University.

    Controlling the properties directly could ultimately make it possible to create fibers that are even stronger than natural ones, because engineers can choose characteristics for a particular use. For example, while spiders may need elasticity so their webs can capture insects without breaking, those designing fibers for use as surgical sutures would need more strength and less stretchiness. “Silk doesn’t give us that choice,” Buehler says.

    The processing of the material can be done at room temperature using water-based solutions, so scaling up manufacturing should be relatively easy, team members say. So far, the fibers they have made in the lab are not as strong as natural spider silk, but now that the basic process has been established, it should be possible to fine-tune the materials and improve its strength, they say.

    “Our goal is to improve the strength, elasticity, and toughness of artificially spun fibers by borrowing bright ideas from nature,” Lin says. This study could inspire the development of new synthetic fibers — or any materials requiring enhanced properties, such as in electrical and thermal transport, in a certain direction.

    “This is an amazing piece of work,” says Huajian Gao, a professor of engineering at Brown University who was not involved in this research. “This could lead to a breakthrough that may allow us to directly explore engineering applications of silk-like materials.”

    Gao adds that the team’s exploration of variations in web structure “may have practical impacts in improving the design of fiber-reinforced composites by significantly increasing their strength and robustness without increasing the weight. The impact on material innovation could be particularly important for aerospace and industrial applications, where light weight is essential.”

    The research was supported by the National Institutes of Health, the National Science Foundation, the Office of Naval Research, the National Research Foundation of Korea, and the European Research Council.

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  • richardmitnick 7:16 am on May 8, 2015 Permalink | Reply
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    From MIT: “Plugging up leaky graphene” 

    MIT News

    May 8, 2015
    Jennifer Chu

    In a two-step process, engineers have successfully sealed leaks in graphene. First, the team fabricated graphene on a copper surface (top left) — a process that can create intrinsic defects in graphene, shown as cracks on the surface. After lifting the graphene and depositing it on a porous surface (top right), the transfer creates further holes and tears. In a first step (bottom left), the team used atomic layer deposition to deposit hafnium (in gray) to seal intrinsic cracks, then plugged the remaining holes (bottom left) with nylon (in red), via interfacial polymerization.
    Courtesy of the researchers.

    For faster, longer-lasting water filters, some scientists are looking to graphene —thin, strong sheets of carbon — to serve as ultrathin membranes, filtering out contaminants to quickly purify high volumes of water.

    Graphene’s unique properties make it a potentially ideal membrane for water filtration or desalination. But there’s been one main drawback to its wider use: Making membranes in one-atom-thick layers of graphene is a meticulous process that can tear the thin material — creating defects through which contaminants can leak.

    Now engineers at MIT, Oak Ridge National Laboratory, and King Fahd University of Petroleum and Minerals (KFUPM) have devised a process to repair these leaks, filling cracks and plugging holes using a combination of chemical deposition and polymerization techniques. The team then used a process it developed previously to create tiny, uniform pores in the material, small enough to allow only water to pass through.

    Combining these two techniques, the researchers were able to engineer a relatively large defect-free graphene membrane — about the size of a penny. The membrane’s size is significant: To be exploited as a filtration membrane, graphene would have to be manufactured at a scale of centimeters, or larger.

    In experiments, the researchers pumped water through a graphene membrane treated with both defect-sealing and pore-producing processes, and found that water flowed through at rates comparable to current desalination membranes. The graphene was able to filter out most large-molecule contaminants, such as magnesium sulfate and dextran.

    Rohit Karnik, an associate professor of mechanical engineering at MIT, says the group’s results, published in the journal Nano Letters, represent the first success in plugging graphene’s leaks.

    “We’ve been able to seal defects, at least on the lab scale, to realize molecular filtration across a macroscopic area of graphene, which has not been possible before,” Karnik says. “If we have better process control, maybe in the future we don’t even need defect sealing. But I think it’s very unlikely that we’ll ever have perfect graphene — there will always be some need to control leakages. These two [techniques] are examples which enable filtration.”

    Sean O’Hern, a former graduate research assistant at MIT, is the paper’s first author. Other contributors include MIT graduate student Doojoon Jang, former graduate student Suman Bose, and Professor Jing Kong.

    A delicate transfer

    “The current types of membranes that can produce freshwater from saltwater are fairly thick, on the order of 200 nanometers,” O’Hern says. “The benefit of a graphene membrane is, instead of being hundreds of nanometers thick, we’re on the order of three angstroms — 600 times thinner than existing membranes. This enables you to have a higher flow rate over the same area.”

    O’Hern and Karnik have been investigating graphene’s potential as a filtration membrane for the past several years. In 2009, the group began fabricating membranes from graphene grown on copper — a metal that supports the growth of graphene across relatively large areas. However, copper is impermeable, requiring the group to transfer the graphene to a porous substrate following fabrication.

    However, O’Hern noticed that this transfer process would create tears in graphene. What’s more, he observed intrinsic defects created during the growth process, resulting perhaps from impurities in the original material.

    Plugging graphene’s leaks

    To plug graphene’s leaks, the team came up with a technique to first tackle the smaller intrinsic defects, then the larger transfer-induced defects. For the intrinsic defects, the researchers used a process called “atomic layer deposition,” placing the graphene membrane in a vacuum chamber, then pulsing in a hafnium-containing chemical that does not normally interact with graphene. However, if the chemical comes in contact with a small opening in graphene, it will tend to stick to that opening, attracted by the area’s higher surface energy.

    The team applied several rounds of atomic layer deposition, finding that the deposited hafnium oxide successfully filled in graphene’s nanometer-scale intrinsic defects. However, O’Hern realized that using the same process to fill in much larger holes and tears — on the order of hundreds of nanometers — would require too much time.

    Instead, he and his colleagues came up with a second technique to fill in larger defects, using a process called “interfacial polymerization” that is often employed in membrane synthesis. After they filled in graphene’s intrinsic defects, the researchers submerged the membrane at the interface of two solutions: a water bath and an organic solvent that, like oil, does not mix with water.

    In the two solutions, the researchers dissolved two different molecules that can react to form nylon. Once O’Hern placed the graphene membrane at the interface of the two solutions, he observed that nylon plugs formed only in tears and holes — regions where the two molecules could come in contact because of tears in the otherwise impermeable graphene — effectively sealing the remaining defects.

    Using a technique they developed last year, the researchers then etched tiny, uniform holes in graphene — small enough to let water molecules through, but not larger contaminants. In experiments, the group tested the membrane with water containing several different molecules, including salt, and found that the membrane rejected up to 90 percent of larger molecules. However, it let salt through at a faster rate than water.

    The preliminary tests suggest that graphene may be a viable alternative to existing filtration membranes, although Karnik says techniques to seal its defects and control its permeability will need further improvements.

    “Water desalination and nanofiltration are big applications where, if things work out and this technology withstands the different demands of real-world tests, it would have a large impact,” Karnik says. “But one could also imagine applications for fine chemical- or biological-sample processing, where these membranes could be useful. And this is the first report of a centimeter-scale graphene membrane that does any kind of molecular filtration. That’s exciting.”

    De-en Jiang, an assistant professor of chemistry at the University of California at Riverside, sees the defect-sealing technique as “a great advance toward making graphene filtration a reality.”

    “The two-step technique is very smart: sealing the defects while preserving the desired pores for filtration,” says Jiang, who did not contribute to the research. “This would make the scale-up much easier. One can produce a large graphene membrane first, not worrying about the defects, which can be sealed later.”

    This research was supported in part by the Center for Clean Water and Clean Energy at MIT and KFUPM, the U.S. Department of Energy, and the National Science Foundation.

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  • richardmitnick 6:59 am on May 8, 2015 Permalink | Reply
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    From MIT: “Electrons corralled using new quantum tool” 

    MIT News

    May 7, 2015
    David L. Chandler

    Image: Jon Wyrick/NIST

    “Whispering gallery” effect confines electrons, could provide basis for new electron-optics devices.

    Researchers have succeeded in creating a new “whispering gallery” effect for electrons in a sheet of graphene — making it possible to precisely control a region that reflects electrons within the material. They say the accomplishment could provide a basic building block for new kinds of electronic lenses, as well as quantum-based devices that combine electronics and optics.

    The new system uses a needle-like probe that forms the basis of present-day scanning tunneling microscopes (STM), enabling control of both the location and the size of the reflecting region within graphene — a two-dimensional form of carbon that is just one atom thick.

    The new finding is described in a paper appearing in the journal Science, co-authored by MIT professor of physics Leonid Levitov and researchers at the National Institute of Standards and Technology (NIST), the University of Maryland, Imperial College London, and the National Institute for Materials Science (NIMS) in Tsukuba, Japan.

    When the sharp tip of the STM is poised over a sheet of graphene, it produces a circular barrier on the sheet that “acts as a perfect curved mirror” for electrons, Levitov says, reflecting them along the curved surface until they begin to interfere with themselves. This controllable reflectivity and interference is similar, he adds, to so-called “whispering gallery” confinement modes that have been used in optical and acoustic systems — but these have not been tunable or adjustable.

    “In optics, whispering gallery resonators are known and useful,” Levitov says. “They provide high-quality cavities that find applications in sensing, spectroscopy, and communications. But the usual problem in optics is they’re not tunable.” Similarly, previous attempts to create quantum “corrals” for electrons have used atoms precisely positioned on a surface, which cannot be reconfigured easily.

    The confinement in this case is produced by the boundary between two different regions on the graphene surface, corresponding to the “p” and “n” regions in a transistor. In this case, a circular region just beneath the STM tip takes on one polarity, and the surrounding region the opposite polarity, creating a controllable circular junction between the two regions. Electrons inside sheets of graphene behave like particles of light; in this case, the circular junction acts as a curved mirror that can focus and control the electrons.

    It’s too early to predict what specific uses might be found for this phenomenon, Levitov says, but adds, “Any resonator can be used for a variety of things.”

    This electron resonator combines several good features. There’s clearly something special about having tunability and also high quality at the same time.”

    Philip Kim, a professor of physics at Harvard University who was not connected with this research, says it is “a very notable example of demonstrating novel electronic properties of graphene.” He adds, “Electrons in graphene behave like photons confined in a two-dimensional atomic sheet. This work unambiguously demonstrates that electrons confined in the potential created by scanning probe microscope exhibit a wave like resonance behavior, known as whispering gallery mode.”

    Because the new system is based on well-established STM technology, it could be developed relatively quickly into usable devices, Levitov suggests. And conveniently, the STM not only creates the whispering gallery effect, but also provides a means of observing the results, to study the phenomenon. “The tip does double-duty in this case,” he says.

    This could be a step toward the creation of electronic lenses, Levitov says — “a concept that intrigues graphene researchers.” In principle, these could provide a way of observing objects one-thousandth the size of those visible using light waves.

    Electronic lenses would represent a fundamentally different approach from existing electron microscopes, which bombard a surface with high-energy beams of electrons, obliterating any subtle effects within the objects being observed. Electron lenses, by contrast, would be able to observe the ambient low-energy electrons within the object itself.

    An appealing feature of the setup developed in NIST is that the boundary between the two surface regions, which can serve as a lens, is movable, since it is carried along with the STM tip when it is scanning the surface. This could make it possible to study “subtle things about how charge carriers behave at a microscopic level, that you can’t see from the outside,” Levitov says.

    The new work by Levitov and his colleagues provides one piece of such a system — and potentially of other advanced electro-optical systems, he says, such as negative-refraction materials that have been proposed as a kind of “invisibility cloak.” The new whispering-gallery mode for electrons is part of a toolbox that could lead to a whole family of new quantum-based electron-optics devices. It could also be used for high-fidelity sensing, since such resonators “can be used to enhance your sensitivity to very small signals,” Levitov says.

    Harvard’s Kim says that this work “is an important step toward building novel electronic applications, based on the unique relativistic quantum-mechanical behavior of electrons in graphene.”

    The research team also included graduate student Joaquin Rodriguez-Nieva from MIT; Yue Zhao, Jonathan Wyrick, Fabian Natterer, Nikolai Zhitenev, and Joseph Stroscio from NIST; Cyprian Lewandowski from Imperial College London; and Kenji Watanabe and Takashi Taniguchi from NIMS.

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  • richardmitnick 12:35 pm on April 8, 2015 Permalink | Reply
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    From MIT: “Biologists identify brain tumor weakness” 

    MIT News

    April 8, 2015
    Anne Trafton

    Discovery could offer a new target for treatment of glioblastoma.

    Temp 1

    The top two panels show tumors produced by cancer cells. The outer ring of cells (blue) has enough oxygen to survive, but not as much oxygen reaches the inner cells. At top right, tumor cells lack the SHMT2 gene and are unable to survive in this central region, as indicated by the pink stain that marks a protein produced during cell death. At top left, the cells express high levels of SHMT2, allowing some of them to survive, indicated by the blue clusters of cells. The bottom two panels are magnifications of the central tumor regions. Courtesy of the researchers

    Biologists at MIT and the Whitehead Institute have discovered a vulnerability of brain cancer cells that could be exploited to develop more-effective drugs against brain tumors.

    The study, led by researchers from the Whitehead Institute and MIT’s Koch Institute for Integrative Cancer Research, found that a subset of glioblastoma tumor cells is dependent on a particular enzyme that breaks down the amino acid glycine. Without this enzyme, toxic metabolic byproducts build up inside the tumor cells, and they die.

    Blocking this enzyme in glioblastoma cells could offer a new way to combat such tumors, says Dohoon Kim, a postdoc at the Whitehead Institute and lead author of the study, which appears in the April 8 online edition of Nature.

    David Sabatini, a professor of biology at MIT and member of the Whitehead Institute, is the paper’s senior author. Matthew Vander Heiden, the Eisen and Chang Career Development Associate Professor of Biology and a member of the Koch Institute, also contributed to the research, along with members of his lab.

    GLDC caught the researchers’ attention as they investigated diseases known as “inborn errors of metabolism,” which occur when cells are missing certain metabolic enzymes. Many of these disorders specifically affect brain development; the most common of these is phenylketonuria, marked by an inability to break down the amino acid phenylalanine. Such patients must avoid eating phenylalanine to prevent problems such as intellectual disability and seizures.

    Loss of GLDC produces a disorder called nonketotic hyperglycinemia, which causes glycine to build up in the brain and can lead to severe mental retardation. GLDC is also often overactive in certain cells of glioblastoma, the most common and most aggressive type of brain tumor found in humans.

    The researchers found that GLDC, which breaks down the amino acid glycine, is overexpressed only in glioblastoma cells that also have high levels of a gene called SHMT2, which converts the amino acid serine into glycine. Those cells are so dependent on GLDC that when they lose it, they die.

    Further investigation revealed that SHMT2 is expressed most highly in cancer cells that live in so-called ischemic regions — areas that are very low in oxygen and nutrients. These regions are often found at the center of tumors, which are inaccessible to blood vessels. It turns out that in this low-oxygen environment, SHMT2 gives cells a survival edge because it can indirectly influence the activity of an enzyme called PKM2, which is part of the cell’s machinery for breaking down glucose.

    Regulation of PKM2 can impact whether cells can generate the material to build new cancer cells, but the same regulation also affects the consumption of oxygen — a scarce resource in ischemic regions.

    “Cells that have high SHMT2 activity have low PKM2 activity, and consequently low oxygen-consumption rates, which makes them better suited to survive in the ischemic tumor microenvironment,” Kim says.

    However, this highly active SHMT2 also produces a glut of glycine, which the cell must break down using GLDC. Without GLDC, glycine enters a different metabolic pathway that generates toxic products that accumulate and kill the cell.

    “An interesting aspect of the current study is that they uncovered why glycine accumulation is toxic,” says Navdeep Chandel, a professor of medicine and cellular biology at Northwestern University who was not part of the research team. “GLDC loss accumulates glycine, causing nonketotic hyperglycinaemia, a disorder that severely affects the developing brain. Sabatini and colleagues elucidated that loss of GLDC builds up glycine levels, resulting in funneling of glycine into metabolic pathways that generate toxic molecules, such as aminoacetone and methylglyoxal.”

    The finding also raises the possibility that these GLDC-dependent cells could be killed with drugs that block GLDC activity, according to the researchers, who are now seeking potential drug compounds that could do just that.

    The research was funded by the American Brain Tumor Association, the National Institutes of Health, and the Koch Institute.

    See the full article here.

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