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  • richardmitnick 12:25 pm on December 12, 2020 Permalink | Reply
    Tags: "Discovery suggests new promise for nonsilicon computer transistors", A single laptop could contain billions of transistors., , , , InGaAs-indium gallium arsenide, MIT News, , Transistors are the building blocks of a classical computer.   

    From MIT News: “Discovery suggests new promise for nonsilicon computer transistors” 

    MIT News

    From MIT News

    December 9, 2020
    Daniel Ackerman

    Once deemed suitable only for high-speed communication systems, an alloy called InGaAs might one day rival silicon in high-performance computing.

    1
    MIT researchers have found that an alloy material called InGaAs could be suitable for high-performance computer transistors. If operated at high-frequencies, InGaAs transistors could one day rival silicon. This image shows a solid state memory wafer traditionally made of silicon.

    For decades, one material has so dominated the production of computer chips and transistors that the tech capital of the world — Silicon Valley — bears its name. But silicon’s reign may not last forever.

    MIT researchers have found that an alloy called InGaAs (indium gallium arsenide) could hold the potential for smaller and more energy efficient transistors. Previously, researchers thought that the performance of InGaAs transistors deteriorated at small scales. But the new study shows this apparent deterioration is not an intrinsic property of the material itself.

    The finding could one day help push computing power and efficiency beyond what’s possible with silicon. “We’re really excited,” said Xiaowei Cai, the study’s lead author. “We hope this result will encourage the community to continue exploring the use of InGaAs as a channel material for transistors.”

    Cai, now with Analog Devices, completed the research as a PhD student in the MIT Microsystems Technology Laboratories and Department of Electrical Engineering and Computer Science (EECS), with Donner Professor Jesús del Alamo. Her co-authors include Jesús Grajal of Polytechnic University of Madrid, as well as MIT’s Alon Vardi and del Alamo. The paper [IEEE Transactions on Electron Devices] will be presented this month at the virtual IEEE International Electron Devices Meeting.

    Transistors are the building blocks of a computer. Their role as switches, either halting electric current or letting it flow, gives rise to a staggering array of computations — from simulating the global climate to playing cat videos on Youtube. A single laptop could contain billions of transistors. For computing power to improve in the future, as it has for decades, electrical engineers will have to develop smaller, more tightly packed transistors. To date, silicon has been the semiconducting material of choice for transistors. But InGaAs has shown hints of becoming a potential competitor.

    Electrons can zip through InGaAs with ease, even at low voltage. The material is “known to have great [electron] transport properties,” says Cai. InGaAs transistors can process signals quickly, potentially resulting in speedier calculations. Plus, InGaAs transistors can operate at relatively low voltage, meaning they could enhance a computer’s energy efficiency. So InGaAs might seem like a promising material for computer transistors. But there’s a catch.

    InGaAs’ favorable electron transport properties seem to deteriorate at small scales — the scales needed to build faster and denser computer processors. The problem has led some researchers to conclude that nanoscale InGaAs transistors simply aren’t suited for the task. But, says Cai, “we have found that that’s a misconception.”

    The team discovered that InGaAs’ small-scale performance issues are due in part to oxide trapping. This phenomenon causes electrons to get stuck while trying to flow through a transistor. “A transistor is supposed to work as a switch. You want to be able to turn a voltage on and have a lot of current,” says Cai. “But if you have electrons trapped, what happens is you turn a voltage on, but you only have a very limited amount of current in the channel. So the switching capability is a lot lower when you have that oxide trapping.”

    Cai’s team pinpointed oxide trapping as the culprit by studying the transistor’s frequency dependence — the rate at which electric pulses are sent through the transistor. At low frequencies, the performance of nanoscale InGaAs transistors appeared degraded. But at frequencies of 1 gigahertz or greater, they worked just fine — oxide trapping was no longer a hindrance. “When we operate these devices at really high frequency, we noticed that the performance is really good,” she says. “They’re competitive with silicon technology.”

    Cai hopes her team’s discovery will give researchers new reason to pursue InGaAs-based computer transistors. The work shows that “the problem to solve is not really the InGaAs transistor itself. It’s this oxide trapping issue,” she says. “We believe this is a problem that can be solved or engineered out of.” She adds that InGaAs has shown promise in both classical and quantum computing applications.

    “This [research] area remains very, very exciting,” says del Alamo. “We thrive on pushing transistors to the extreme of performance.” One day, that extreme performance could come courtesy of InGaAs.

    This research was supported in part by the Defense Threat Reduction Agency and the National Science Foundation.

    See the full article here .


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  • richardmitnick 3:23 pm on July 26, 2020 Permalink | Reply
    Tags: "An origin story for a family of oddball meteorites", A family of meteorites has befuddled researchers since its discovery in the 1960s, , , , , If the magnetic field was generated by the parent body’s core this would mean that the fragments that ultimately fell to Earth could not have come from the core itself., MIT News, The parent body of these rare meteorites was indeed a multilayered differentiated object that likely had a liquid metallic core., There has been little evidence in the meteorite record of intermediate objects with both melted and unmelted compositions except for a rare family of meteorites called IIE irons.   

    From MIT News: “An origin story for a family of oddball meteorites” 

    MIT News

    From MIT News

    July 24, 2020
    Jennifer Chu

    1
    Samples from a rare meteorite family, including the one shown here, reveal that their parent planetesimal, formed in the earliest stages of the solar system, was a complex, layered object, with a molten core and solid crust similar to Earth.

    Photo credit: Carl Agee, Institute of Meteoritics, University of New Mexico. Background edited by MIT News.

    Most meteorites that have landed on Earth are fragments of planetesimals, the very earliest protoplanetary bodies in the solar system. Scientists have thought that these primordial bodies either completely melted early in their history or remained as piles of unmelted rubble.

    But a family of meteorites has befuddled researchers since its discovery in the 1960s. The diverse fragments, found all over the world, seem to have broken off from the same primordial body, and yet the makeup of these meteorites indicates that their parent must have been a puzzling chimera that was both melted and unmelted.

    Now researchers at MIT and elsewhere have determined that the parent body of these rare meteorites was indeed a multilayered, differentiated object that likely had a liquid metallic core. This core was substantial enough to generate a magnetic field that may have been as strong as Earth’s magnetic field is today.

    Their results, published today in the journal Science Advances, suggest that the diversity of the earliest objects in the solar system may have been more complex than scientists had assumed.

    “This is one example of a planetesimal that must have had melted and unmelted layers. It encourages searches for more evidence of composite planetary structures,” says lead author Clara Maurel, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “Understanding the full spectrum of structures, from nonmelted to fully melted, is key to deciphering how planetesimals formed in the early solar system.”

    Maurel’s co-authors include EAPS Professor Benjamin Weiss, along with collaborators at Oxford University, Cambridge University, the University of Chicago, Lawrence Berkeley National Laboratory, and the Southwest Research Institute.

    Oddball irons

    The solar system formed around 4.5 billion years ago as a swirl of super-hot gas and dust. As this disk gradually cooled, bits of matter collided and merged to form progressively larger bodies, such as planetesimals.

    The majority of meteorites that have fallen to Earth have compositions that suggest they came from such early planetesimals that were either of two types: melted, and unmelted. Both types of objects, scientists believe, would have formed relatively quickly, in less than a few million years, early in the solar system’s evolution.

    If a planetesimal formed in the first 1.5 million years of the solar system, short-lived radiogenic elements could have melted the body entirely due to the heat released by their decay. Unmelted planetesimals could have formed later, when their material had lower quantities of radiogenic elements, insufficient for melting.

    There has been little evidence in the meteorite record of intermediate objects with both melted and unmelted compositions, except for a rare family of meteorites called IIE irons.

    “These IIE irons are oddball meteorites,” Weiss says. “They show both evidence of being from primordial objects that never melted, and also evidence for coming from a body that’s completely or at least substantially melted. We haven’t known where to put them, and that’s what made us zero in on them.”

    Magnetic pockets

    Scientists have previously found that both melted and unmelted IIE meteorites originated from the same ancient planetesimal, which likely had a solid crust overlying a liquid mantle, like Earth. Maurel and her colleagues wondered whether the planetesimal also may have harbored a metallic, melted core.

    “Did this object melt enough that material sank to the center and formed a metallic core like that of the Earth?” Maurel says. “That was the missing piece to the story of these meteorites.”

    The team reasoned that if the planetesimal did host a metallic core, it could very well have generated a magnetic field, similar to the way Earth’s churning liquid core produces a magnetic field. Such an ancient field could have caused minerals in the planetesimal to point in the direction of the field, like a needle in a compass. Certain minerals could have kept this alignment over billions of years.

    Maurel and her colleagues wondered whether they might find such minerals in samples of IIE meteorites that had crashed to Earth. They obtained two meteorites, which they analyzed for a type of iron-nickel mineral known for its exceptional magnetism-recording properties.

    The team analyzed the samples using the Lawrence Berkeley National Laboratory’s Advanced Light Source, which produces X-rays that interact with mineral grains at the nanometer scale, in a way that can reveal the minerals’ magnetic direction.

    LBNL ALS

    Sure enough, the electrons within a number of grains were aligned in a similar direction — evidence that the parent body generated a magnetic field, possibly up to several tens of microtesla, which is about the strength of Earth’s magnetic field. After ruling out less plausible sources, the team concluded that the magnetic field was most likely produced by a liquid metallic core. To generate such a field, they estimate the core must have been at least several tens of kilometers wide.

    Such complex planetesimals with mixed composition (both melted, in the form of a liquid core and mantle, and unmelted in the form of a solid crust), Maurel says, would likely have taken over several million years to form — a formation period that is longer than what scientists had assumed until recently.

    But where within the parent body did the meteorites come from? If the magnetic field was generated by the parent body’s core, this would mean that the fragments that ultimately fell to Earth could not have come from the core itself. That’s because a liquid core only generates a magnetic field while still churning and hot. Any minerals that would have recorded the ancient field must have done so outside the core, before the core itself completely cooled.

    Working with collaborators at the University of Chicago, the team ran high-velocity simulations of various formation scenarios for these meteorites. They showed that it was possible for a body with a liquid core to collide with another object, and for that impact to dislodge material from the core. That material would then migrate to pockets close to the surface where the meteorites originated.

    “As the body cools, the meteorites in these pockets will imprint this magnetic field in their minerals. At some point, the magnetic field will decay, but the imprint will remain,” Maurel says. “Later on, this body is going to undergo a lot of other collisions until the ultimate collisions that will place these meteorites on Earth’s trajectory.”

    Was such a complex planetesimal an outlier in the early solar system, or one of many such differentiated objects? The answer, Weiss says, may lie in the asteroid belt, a region populated with primordial remnants.

    “Most bodies in the asteroid belt appear unmelted on their surface,” Weiss says. “If we’re eventually able to see inside asteroids, we might test this idea. Maybe some asteroids are melted inside, and bodies like this planetesimal are actually common.”

    This research was funded, in part, by NASA.

    See the full article here .


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  • richardmitnick 3:04 pm on July 25, 2020 Permalink | Reply
    Tags: "How to grow a cosmic magnetic field", , , , Cosmic magnetic fields, , Inverse cascade, , MIT Department of Nuclear Science and Engineering., MIT News, , ,   

    From MIT News: Women STEM – “How to grow a cosmic magnetic field” Muni Zhou 

    MIT News

    From MIT News

    July 21, 2020
    Paul Rivenberg | Plasma Science and Fusion Center

    1
    “Physics teaches us not only about what happens at the edge of the universe, but about what we observe in our environment every day, including our technology,” says PhD candidate Muni Zhou. Photo: Paul Rivenberg

    Graduate student Muni Zhou shows how tiny magnetic seed fields can expand to cosmic proportions.

    When Muni Zhou looks into a clear night sky, she might be focusing less on the stars and more on what cannot be seen with the eye. The MIT graduate student, now in her fourth year at the Plasma Science and Fusion Center (PSFC), is fascinated by vast magnetic field structures that exist not only around planets like Earth, but beyond the heliosphere to the edges of the universe. How these cosmic magnetic fields originated and evolved is the longstanding theoretical puzzle she is helping to solve.

    Zhou’s interest in physics developed as a teenager in Shenzhen, China, one of the country’s technology hubs.

    “Physics teaches us not only about what happens at the edge of the universe, but about what we observe in our environment every day, including our technology,” she says. “It helps me understand the world around me.”

    As an undergraduate student at Zhejiang University she explored several fields of physics, eventually focusing on plasma science, excited by its application to fusion research with its potential for producing a reliable supply of carbon-free energy.

    Her fascination with the topic increased while working with the supportive community at the university’s Institute of Fusion Theory and Simulation (IFTS).

    A chance to be an exchange student at Princeton Plasma Physics Laboratory (PPPL) provided Zhou with her first serious research opportunity. The project focused on the physics of a tokamak, a fusion device that uses strong magnetic fields to contain and shape plasma while it is heated to extreme temperatures.

    PPPL NSTX-U

    The study, and the subsequent undergraduate thesis it generated, prepared her for similar research at MIT in the Department of Nuclear Science and Engineering. With the guidance of her advisor, Professor Nuno Loureiro, her plasma research has taken an astrophysical turn, resulting in an article about cosmic magnetic structures, recently published in the Journal of Plasma Physics. NASA also acknowledged Zhou’s research with a Future Investigators of NASA Earth and Space Science Technology (FINESST) grant, which supports graduate student-designed projects that help to further the Science Mission Directorate’s science, technology, and exploration goals.

    Magnetic fields are ubiquitous in the universe.

    3
    Magnetic fields are created around moving charged particles

    They are dynamically important, participating in the formation of stars and galaxies. Cosmic magnetic fields possess intriguing gigantic-scale coherent structures.

    6
    Magnetic field data from the Whirlpool Galaxy, M51. Credit: MPIfR Bonn.

    Zhou explains that these structures could possibly evolve from miniscule-scale magnetic “seed fields,” which are generated by instabilities in the plasma medium that is part of astrophysical systems throughout the universe.

    “In supernova explosions, gamma-ray-burst jets or large-scale accretion shocks at the outskirts of galaxies during early stages of galaxy formation, these magnetic seed fields form at microscopic scales,” says Zhou. “But these tiny fields, through interaction with plasmas, can potentially increase their coherence length by many orders of magnitude to become the enormous astronomical-scale magnetic fields observed in the universe.”

    This so called “inverse cascade,” the process by which a magnetic field grows from small to large scale, is crucial in forming cosmic-scale magnetic fields.

    Zhou’s research is dependent on conceptualizing this plasma system with its seed fields as a sea of flux ropes — ropelike plasma structures threaded by magnetic field lines.

    “Now that we have simplified this complex astrophysical phenomenon to an idealized concept we can investigate,” she says, “the question becomes, what are the dynamics of this large ensemble of magnetic flux ropes? And can their interactions expand a small-scale magnetic field to much larger scales?”

    Zhou and her colleagues have found that the growth of a magnetic field’s scale depends on the coalescence of these flux ropes. This is facilitated by the process of magnetic reconnection, in which oppositely-directed magnetic field lines tear and reconnect, releasing magnetic energy.

    NASA Magnetic reconnection, Credit: M. Aschwanden et al. (LMSAL), TRACE, NASA

    When two flux ropes interact, their field lines reconnect, merging into a larger flux rope and expanding the scale of the magnetic field.

    When Zhou tested the phenomenon with supercomputer simulations, she observed that the system rapidly became chaotic when the flux ropes began interacting, developing an unconventional type of turbulence. Nevertheless, she was still able to observe the expansion of magnetic fields. The analytical model suggests that this interaction of flux-ropes can grow the magnetic field to larger scales.

    Loureiro, whose National Science Foundation CAREER Award funds this research, is impressed with Zhou and her results, noting that in their discussions she already feels more like a colleague than a student.

    “The problem she is working on is very hard, and yet she’s already made more progress on it than I could have reasonably expected,” he says. “I feel like this paper of hers really is a fundamental contribution that will be very impactful.”

    Zhou feels the results have a kind of beauty.

    “It is very elegant, to me,” she says. “In such a complex turbulent system, the plasmas self-organize. As a result, we see the formation of large-scale magnetic structures. It is a beautiful example of how order can emerge from chaos.”

    See the full article here .


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  • richardmitnick 2:53 pm on July 16, 2020 Permalink | Reply
    Tags: "In a first astronomers watch a black hole’s corona disappear then reappear", , , , , , MIT News   

    From MIT News: “In a first, astronomers watch a black hole’s corona disappear, then reappear” 

    MIT News

    From MIT News

    July 15, 2020
    Jennifer Chu

    1
    Astronomers at MIT and elsewhere watched a black hole’s corona disappear, then reappear, for first time. A colliding star may have triggered the drastic transformation. Image credit: NASA/JPL-Caltech

    A colliding star may have triggered the drastic transformation.

    It seems the universe has an odd sense of humor. While a crown-encrusted virus has run roughshod over the world, another entirely different corona about 100 million light years from Earth has mysteriously disappeared.

    For the first time, astronomers at MIT and elsewhere have watched as a supermassive black hole’s own corona, the ultrabright, billion-degree ring of high-energy particles that encircles a black hole’s event horizon, was abruptly destroyed.

    The cause of this dramatic transformation is unclear, though the researchers guess that the source of the calamity may have been a star caught in the black hole’s gravitational pull. Like a pebble tossed into a gearbox, the star may have ricocheted through the black hole’s disk of swirling material, causing everything in the vicinity, including the corona’s high-energy particles, to suddenly plummet into the black hole.

    The result, as the astronomers observed, was a precipitous and surprising drop in the black hole’s brightness, by a factor of 10,000, in under just one year.

    “We expect that luminosity changes this big should vary on timescales of many thousands to millions of years,” says Erin Kara, assistant professor of physics at MIT. “But in this object, we saw it change by 10,000 over a year, and it even changed by a factor of 100 in eight hours, which is just totally unheard of and really mind-boggling.”

    Following the corona’s disappearance, astronomers continued to watch as the black hole began to slowly pull together material from its outer edges to reform its swirling accretion disk, which in turn began to spin up high-energy X-rays close to the black hole’s event horizon. In this way, in just a few months, the black hole was able to generate a new corona, almost back to its original luminosity.

    “This seems to be the first time we’ve ever seen a corona first of all disappear, but then also rebuild itself, and we’re watching this in real-time,” Kara says. “This will be really important to understanding how a black hole’s corona is heated and powered in the first place.”

    Kara and her co-authors, including lead author Claudio Ricci of Universidad Diego Portales in Santiago, Chile, have published their findings today in The Astrophysical Journal Letters. Co-authors from MIT include Ron Remillard, and Dheeraj Pasham.

    A nimble washing machine

    In March 2018, an unexpected burst lit up the view of ASSASN, the All-Sky Automated Survey for Super-Novae, that surveys the entire night sky for supernova activity.

    All Sky Automated Survey for Supernovae located at Las Campanas Observatory in Chile, over 2,500 m (8,200 ft) high (since 1997) and the other on Haleakala, Maui (since 2006), Altitude 3,052 m (10,013 ft)

    The survey recorded a flash from 1ES 1927+654, an active galactic nucleus, or AGN, that is a type of supermassive black hole with higher-than-normal brightness at the center of a galaxy. ASSASN observed that the object’s brightness jumped to about 40 times its normal luminosity.

    “This was an AGN that we sort of knew about, but it wasn’t very special,” Kara says. “Then they noticed that this run-of-the-mill AGN became suddenly bright, which got our attention, and we started pointing lots of other telescopes in lots of other wavelengths to look at it.”

    The team used multiple telescopes to observe the black hole in the X-ray, optical, and ultraviolet wave bands. Most of these telescopes were pointed at the the black hole periodically, for example recording observations for an entire day, every six months. The team also watched the black hole daily with NASA’s NICER, a much smaller X-ray telescope, that is installed aboard the International Space Station, with detectors developed and built by researchers at MIT.

    NASA/NICER on the ISS

    “NICER is great because it’s so nimble,” Kara says. “It’s this little washing machine bouncing around the ISS, and it can collect a ton of X-ray photons. Every day, NICER could take a quick little look at this AGN, then go off and do something else.”

    With frequent observations, the researchers were able to catch the black hole as it precipitously dropped in brightness, in virtually all the wave bands they measured, and especially in the high-energy X-ray band — an observation that signaled that the black hole’s corona had completely and suddenly vaporized.

    “After ASSASN saw it go through this huge crazy outburst, we watched as the corona disappeared,” Kara recalls. “It became undetectable, which we have never seen before.”

    A jolting flash

    Physicists are unsure exactly what causes a corona to form, but they believe it has something to do with the configuration of magnetic field lines that run through a black hole’s accretion disk. At the outer regions of a black hole’s swirling disk of material, magnetic field lines are more or less in a straightforward configuration. Closer in, and especially near the event horizon, material circles with more energy, in a way that may cause magnetic field lines to twist and break, then reconnect. This tangle of magnetic energy could spin up particles swirling close to the black hole, to the level of high-energy X-rays, forming the crown-like corona that encircles the black hole.

    Kara and her colleagues believe that if a wayward star was indeed the culprit in the corona’s disappearance, it would have first been shredded apart by the black hole’s gravitational pull, scattering stellar debris across the accretion disk. This may have caused the temporary flash in brightness that ASSASN captured. This “tidal disruption,” as astronomers call such a jolting event, would have triggered much of the material in the disk to suddenly fall into the black hole. It also might have thrown the disk’s magnetic field lines out of whack in a way that it could no longer generate and support a high-energy corona.

    This last point is a potentially important one for understanding how coronas first form. Depending on the mass of a black hole, there is a certain radius within which a star will most certainly be pulled in by a black hole’s gravity.

    “What that tells us is that, if all the action is happening within that tidal disruption radius, that means the magnetic field configuration that’s supporting the corona must be within that radius,” Kara says. “Which means that, for any normal corona, the magnetic fields within that radius are what’s responsible for creating a corona.”

    The researchers calculated that if a star indeed was the cause of the black hole’s missing corona, and if a corona were to form in a supermassive black hole of similar size, it would do so within a radius of about 4 light minutes — a distance that roughly translates to about 75 million kilometers from the black hole’s center.

    “With the caveat that this event happened from a stellar tidal disruption, this would be some of the strictest constraints we have on where the corona must exist,” Kara says.

    The corona has since reformed, lighting up in high-energy X-rays which the team was also able to observe. It’s not as bright as it once was, but the researchers are continuing to monitor it, though less frequently, to see what more this system has in store.

    “We want to keep an eye on it,” Kara says. “It’s still in this unusual high-flux state, and maybe it’ll do something crazy again, so we don’t want to miss that.”

    See the full article here. .


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  • richardmitnick 8:14 am on August 20, 2018 Permalink | Reply
    Tags: , , Lincoln Laboratory undersea optical communications, , MIT News,   

    From MIT News: “Advancing undersea optical communications” 

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    MIT Widget

    From MIT News

    1
    A remotely operated vehicle and undersea terminal emits a coarse acquisition stabilized beam after locking onto another lasercom terminal. Photo: Nicole Fandel

    2
    Staff performed tests with the undersea optical communications system at the Boston Sports Club pool in Lexington, proving that two underwater vehicles could efficiently search and locate each other. After detecting the remote terminal’s beacon, the local terminal is able to lock on and pull into coarse track in less than one second. Photo courtesy of the research team.

    Lincoln Laboratory researchers are applying narrow-beam laser technology to enable communications between underwater vehicles.

    Nearly five years ago, NASA and Lincoln Laboratory made history when the Lunar Laser Communication Demonstration (LLCD) used a pulsed laser beam to transmit data from a satellite orbiting the moon to Earth — more than 239,000 miles — at a record-breaking download speed of 622 megabits per second.


    MIT Lincoln Laboratory

    Now, researchers at Lincoln Laboratory are aiming to once again break new ground by applying the laser beam technology used in LLCD to underwater communications.

    “Both our undersea effort and LLCD take advantage of very narrow laser beams to deliver the necessary energy to the partner terminal for high-rate communication,” says Stephen Conrad, a staff member in the Control and Autonomous Systems Engineering Group, who developed the pointing, acquisition, and tracking (PAT) algorithm for LLCD. “In regard to using narrow-beam technology, there is a great deal of similarity between the undersea effort and LLCD.”

    However, undersea laser communication (lasercom) presents its own set of challenges. In the ocean, laser beams are hampered by significant absorption and scattering, which restrict both the distance the beam can travel and the data signaling rate. To address these problems, the Laboratory is developing narrow-beam optical communications that use a beam from one underwater vehicle pointed precisely at the receive terminal of a second underwater vehicle.

    This technique contrasts with the more common undersea communication approach that sends the transmit beam over a wide angle but reduces the achievable range and data rate. “By demonstrating that we can successfully acquire and track narrow optical beams between two mobile vehicles, we have taken an important step toward proving the feasibility of the laboratory’s approach to achieving undersea communication that is 10,000 times more efficient than other modern approaches,” says Scott Hamilton, leader of the Optical Communications Technology Group, which is directing this R&D into undersea communication.

    Most above-ground autonomous systems rely on the use of GPS for positioning and timing data; however, because GPS signals do not penetrate the surface of water, submerged vehicles must find other ways to obtain these important data. “Underwater vehicles rely on large, costly inertial navigation systems, which combine accelerometer, gyroscope, and compass data, as well as other data streams when available, to calculate position,” says Thomas Howe of the research team. “The position calculation is noise sensitive and can quickly accumulate errors of hundreds of meters when a vehicle is submerged for significant periods of time.”

    This positional uncertainty can make it difficult for an undersea terminal to locate and establish a link with incoming narrow optical beams. For this reason, “We implemented an acquisition scanning function that is used to quickly translate the beam over the uncertain region so that the companion terminal is able to detect the beam and actively lock on to keep it centered on the lasercom terminal’s acquisition and communications detector,” researcher Nicolas Hardy explains. Using this methodology, two vehicles can locate, track, and effectively establish a link, despite the independent movement of each vehicle underwater.

    Once the two lasercom terminals have locked onto each other and are communicating, the relative position between the two vehicles can be determined very precisely by using wide bandwidth signaling features in the communications waveform. With this method, the relative bearing and range between vehicles can be known precisely, to within a few centimeters, explains Howe, who worked on the undersea vehicles’ controls.

    To test their underwater optical communications capability, six members of the team recently completed a demonstration of precision beam pointing and fast acquisition between two moving vehicles in the Boston Sports Club pool in Lexington, Massachusetts. Their tests proved that two underwater vehicles could search for and locate each other in the pool within one second. Once linked, the vehicles could potentially use their established link to transmit hundreds of gigabytes of data in one session.

    This summer, the team is traveling to regional field sites to demonstrate this new optical communications capability to U.S. Navy stakeholders. One demonstration will involve underwater communications between two vehicles in an ocean environment — similar to prior testing that the Laboratory undertook at the Naval Undersea Warfare Center in Newport, Rhode Island, in 2016. The team is planning a second exercise to demonstrate communications from above the surface of the water to an underwater vehicle — a proposition that has previously proven to be nearly impossible.

    The undersea communication effort could tap into innovative work conducted by other groups at the laboratory. For example, integrated blue-green optoelectronic technologies, including gallium nitride laser arrays and silicon Geiger-mode avalanche photodiode array technologies, could lead to lower size, weight, and power terminal implementation and enhanced communication functionality.

    In addition, the ability to move data at megabit-to gigabit-per-second transfer rates over distances that vary from tens of meters in turbid waters to hundreds of meters in clear ocean waters will enable undersea system applications that the laboratory is exploring.

    Howe, who has done a significant amount of work with underwater vehicles, both before and after coming to the laboratory, says the team’s work could transform undersea communications and operations. “High-rate, reliable communications could completely change underwater vehicle operations and take a lot of the uncertainty and stress out of the current operation methods.”

    See the full article here .


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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

    1
    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.

    See the full article here .

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  • richardmitnick 8:03 am on August 7, 2015 Permalink | Reply
    Tags: , , MIT News   

    From MIT: “How chronic inflammation can lead to cancer” 


    MIT News

    August 7, 2015
    Helen Knight, MIT News correspondent

    1
    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

    2
    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

    3
    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
    Tags: , , , MIT News,   

    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.

    1
    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
    NASA/Kepler

    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.

    NASA TESS
    NASA/TESS

    “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

    1
    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
    Tags: , , , MIT News   

    From MIT: “Small thunderstorms may add up to massive cyclones on Saturn” 


    MIT News

    June 15, 2015
    Jennifer Chu | MIT News Office

    1
    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
    Cassini

    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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