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  • richardmitnick 8:14 pm on September 21, 2014 Permalink | Reply
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    From M.I.T.: “Magnetic fields make the excitons go ’round” 


    MIT News

    September 21, 2014
    David L. Chandler | MIT News Office

    A major limitation in the performance of solar cells happens within the photovoltaic material itself: When photons strike the molecules of a solar cell, they transfer their energy, producing quasi-particles called excitons — an energized state of molecules. That energized state can hop from one molecule to the next until it’s transferred to electrons in a wire, which can light up a bulb or turn a motor.

    temp

    But as the excitons hop through the material, they are prone to getting stuck in minuscule defects, or traps — causing them to release their energy as wasted light.

    Now a team of researchers at MIT and Harvard University has found a way of rendering excitons immune to these traps, possibly improving photovoltaic devices’ efficiency. The work is described in a paper in the journal Nature Materials.

    Their approach is based on recent research on exotic electronic states known as topological insulators, in which the bulk of a material is an electrical insulator — that is, it does not allow electrons to move freely — while its surface is a good conductor.

    The MIT-Harvard team used this underlying principle, called topological protection, but applied it to excitons instead of electrons, explains lead author Joel Yuen, a postdoc in MIT’s Center for Excitonics, part of the Research Laboratory of Electronics. Topological protection, he says, “has been a very popular idea in the physics and materials communities in the last few years,” and has been successfully applied to both electronic and photonic materials.

    Moving on the surface

    Topological excitons would move only at the surface of a material, Yuen explains, with the direction of their motion determined by the direction of an applied magnetic field. In that respect, their behavior is similar to that of topological electrons or photons.

    In its theoretical analysis, the team studied the behavior of excitons in an organic material, a porphyrin thin film, and determined that their motion through the material would be immune to the kind of defects that tend to trap excitons in conventional solar cells.

    The choice of porphyrin for this analysis was based on the fact that it is a well-known and widely studied family of materials, says co-author Semion Saikin, a postdoc at Harvard and an affiliate of the Center for Excitonics. The next step, he says, will be to extend the analysis to other kinds of materials.

    por
    Structure of porphine, the simplest porphyrin

    While the work so far has been theoretical, experimentalists are eager to pursue the concept. Ultimately, this approach could lead to novel circuits that are similar to electronic devices but based on controlling the flow of excitons rather that electrons, Yuen says. “If there are ever excitonic circuits,” he says, “this could be the mechanism” that governs their functioning. But the likely first application of the work would be in creating solar cells that are less vulnerable to the trapping of excitons.

    Eric Bittner, a professor of chemistry at the University of Houston who was not associated with this work, says, “The work is interesting on both the fundamental and practical levels. On the fundamental side, it is intriguing that one may be able to create excitonic materials with topological properties. This opens a new avenue for both theoretical and experimental work. … On the practical side, the interesting properties of these materials and the fact that we’re talking about pretty simple starting components — porphyrin thin films — makes them novel materials for new devices.”

    The work received support from the U.S. Department of Energy and the Defense Threat Reduction Agency. Norman Yao, a graduate student at Harvard, was also a co-author.

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  • richardmitnick 7:53 pm on September 21, 2014 Permalink | Reply
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    From M.I.T.: “New formulation leads to improved liquid battery” 


    MIT News

    September 21, 2014
    David L. Chandler | MIT News Office

    Cheaper, longer-lasting materials could enable batteries that make wind and solar energy more competitive.

    temp

    Researchers at MIT have improved a proposed liquid battery system that could enable renewable energy sources to compete with conventional power plants.

    Donald Sadoway and colleagues have already started a company to produce electrical-grid-scale liquid batteries, whose layers of molten material automatically separate due to their differing densities. But the new formula — published in the journal Nature by Sadoway, former postdocs Kangli Wang and Kai Jiang, and seven others — substitutes different metals for the molten layers used in a battery previously developed by the team.

    Sadoway, the John F. Elliott Professor of Materials Chemistry, says the new formula allows the battery to work at a temperature more than 200 degrees Celsius lower than the previous formulation. In addition to the lower operating temperature, which should simplify the battery’s design and extend its working life, the new formulation will be less expensive to make, he says.

    The battery uses two layers of molten metal, separated by a layer of molten salt that acts as the battery’s electrolyte (the layer that charged particles pass through as the battery is charged or discharged). Because each of the three materials has a different density, they naturally separate into layers, like oil floating on water.

    The original system, using magnesium for one of the battery’s electrodes and antimony for the other, required an operating temperature of 700 C. But with the new formulation, with one electrode made of lithium and the other a mixture of lead and antimony, the battery can operate at temperatures of 450 to 500 C.

    Extensive testing has shown that even after 10 years of daily charging and discharging, the system should retain about 85 percent of its initial efficiency — a key factor in making such a technology an attractive investment for electric utilities.

    Currently, the only widely used system for utility-scale storage of electricity is pumped hydro, in which water is pumped uphill to a storage reservoir when excess power is available, and then flows back down through a turbine to generate power when it is needed. Such systems can be used to match the intermittent production of power from irregular sources, such as wind and solar power, with variations in demand. Because of inevitable losses from the friction in pumps and turbines, such systems return about 70 percent of the power that is put into them (which is called the “round-trip efficiency”).

    Sadoway says his team’s new liquid-battery system can already deliver the same 70 percent efficiency, and with further refinements may be able to do better. And unlike pumped hydro systems — which are only feasible in locations with sufficient water and an available hillside — the liquid batteries could be built virtually anywhere, and at virtually any size. “The fact that we don’t need a mountain, and we don’t need lots of water, could give us a decisive advantage,” Sadoway says.

    The biggest surprise for the researchers was that the antimony-lead electrode performed so well. They found that while antimony could produce a high operating voltage, and lead gave a low melting point, a mixture of the two combined both advantages, with a voltage as high as antimony alone, and a melting point between that of the two constituents — contrary to expectations that lowering the melting point would come at the expense of also reducing the voltage.

    “We hoped [the characteristics of the two metals] would be nonlinear,” Sadoway says — that is, that the operating voltage would not end up halfway between that of the two individual metals. “They proved to be [nonlinear], but beyond our imagination. There was no decline in the voltage. That was a stunner for us.”

    Not only did that provide significantly improved materials for the group’s battery system, but it opens up whole new avenues of research, Sadoway says. Going forward, the team will continue to search for other combinations of metals that might provide even lower-temperature, lower-cost, and higher-performance systems. “Now we understand that liquid metals bond in ways that we didn’t understand before,” he says.

    With this fortuitous finding, Sadoway says, “Nature tapped us on the shoulder and said, ‘You know, there’s a better way!’” And because there has been little commercial interest in exploring the properties and potential uses of liquid metals and alloys of the type that are most attractive as electrodes for liquid metal batteries, he says, “I think there’s still room for major discoveries in this field.”

    Robert Metcalfe, professor of innovation at the University of Texas at Austin, who was not involved in this work, says, “The Internet gave us cheap and clean connectivity using many kinds of digital storage. Similarly, we will solve cheap and clean energy with many kinds of storage. Energy storage will absorb the increasing randomness of energy supply and demand, shaving peaks, increasing availability, improving efficiency, lowering costs.”

    Metcalfe adds that Sadoway’s approach to storage using liquid metals “is very promising.”

    The research was supported by the U.S. Department of Energy’s Advanced Research Projects Agency-Energy and by French energy company Total.

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  • richardmitnick 12:15 pm on September 19, 2014 Permalink | Reply
    Tags: , Mechanical Engineering, MIT News   

    From M.I.T.: “Fingertip sensor gives robot unprecedented dexterity” 


    MIT News

    September 19, 2014
    Larry Hardesty | MIT News Office

    Researchers at MIT and Northeastern University have equipped a robot with a novel tactile sensor that lets it grasp a USB cable draped freely over a hook and insert it into a USB port.

    hook
    Armed with the GelSight sensor, a robot can grasp a freely hanging USB cable and plug it into a USB port. Photo: Melanie Gonick/MIT

    The sensor is an adaptation of a technology called GelSight, which was developed by the lab of Edward Adelson, the John and Dorothy Wilson Professor of Vision Science at MIT, and first described in 2009. The new sensor isn’t as sensitive as the original GelSight sensor, which could resolve details on the micrometer scale. But it’s smaller — small enough to fit on a robot’s gripper — and its processing algorithm is faster, so it can give the robot feedback in real time.

    gel

    Industrial robots are capable of remarkable precision when the objects they’re manipulating are perfectly positioned in advance. But according to Robert Platt, an assistant professor of computer science at Northeastern and the research team’s robotics expert, for a robot taking its bearings as it goes, this type of fine-grained manipulation is unprecedented.

    “People have been trying to do this for a long time,” Platt says, “and they haven’t succeeded because the sensors they’re using aren’t accurate enough and don’t have enough information to localize the pose of the object that they’re holding.”

    The researchers presented their results at the International Conference on Intelligent Robots and Systems this week. The MIT team — which consists of Adelson; first author Rui Li, a PhD student; Wenzhen Yuan, a master’s student; and Mandayam Srinivasan, a senior research scientist in the Department of Mechanical Engineering — designed and built the sensor. Platt’s team at Northeastern, which included Andreas ten Pas and Nathan Roscup, developed the robotic controller and conducted the experiments.

    Synesthesia

    Whereas most tactile sensors use mechanical measurements to gauge mechanical forces, GelSight uses optics and computer-vision algorithms.

    “I got interested in touch because I had children,” Adelson says. “I expected to be fascinated by watching how they used their visual systems, but I was actually more fascinated by how they used their fingers. But since I’m a vision guy, the most sensible thing, if you wanted to look at the signals coming into the finger, was to figure out a way to transform the mechanical, tactile signal into a visual signal — because if it’s an image, I know what to do with it.”

    A GelSight sensor — both the original and the new, robot-mounted version — consists of a slab of transparent, synthetic rubber coated on one side with a metallic paint. The rubber conforms to any object it’s pressed against, and the metallic paint evens out the light-reflective properties of diverse materials, making it much easier to make precise optical measurements.

    In the new device, the gel is mounted in a cubic plastic housing, with just the paint-covered face exposed. The four walls of the cube adjacent to the sensor face are translucent, and each conducts a different color of light — red, green, blue, or white — emitted by light-emitting diodes at the opposite end of the cube. When the gel is deformed, light bounces off of the metallic paint and is captured by a camera mounted on the same cube face as the diodes.

    From the different intensities of the different-colored light, the algorithms developed by Adelson’s team can infer the three-dimensional structure of ridges or depressions of the surface against which the sensor is pressed.

    Although there was a 3-millimeter variation in where the robot grasped the plug, it was still able to measure its position accurately enough to insert it into a USB port that tolerated only about a millimeter’s error. By that measure, even the lower-resolution, robot-mounted version of the GelSight sensor is about 100 times more sensitive than a human finger.

    Plug ‘n play

    In Platt’s experiments, a Baxter robot from MIT spinout Rethink Robotics was equipped with a two-pincer gripper, one of whose pincers had a GelSight sensor on its tip. Using conventional computer-vision algorithms, the robot identified the dangling USB plug and attempted to grasp it. It then determined the position of the USB plug relative to its gripper from an embossed USB symbol. Although there was a 3-millimeter variation, in each of two dimensions, in where the robot grasped the plug, it was still able to insert it into a USB port that tolerated only about a millimeter’s error.

    “Having a fast optical sensor to do this kind of touch sensing is a novel idea,” says Daniel Lee, a professor of electrical and systems engineering at the University of Pennsylvania and director of the GRASP robotics lab, “and I think the way that they’re doing it with such low-cost components — using just basically colored LEDs and a standard camera — is quite interesting.”

    How GelSight fares against other approaches to tactile sensing will depend on “the application domain and what the price points are,” Lee says. “What Rui’s device has going for it is that it has very good spatial resolution. It’s able to see heights on the level of tens of microns. Compared to other devices in the domain that use things like barometers, the spatial resolution is very good.”

    “As roboticists, we are always looking for new sensors,” Lee adds. “This is a promising prototype. It could be developed into practical device.”

    See the full article, with video, here.

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  • richardmitnick 11:39 am on September 16, 2014 Permalink | Reply
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    From M.I.T.: “Neuroscientists identify key role of language gene” 


    MIT News

    September 15, 2014
    Anne Trafton | MIT News Office

    Neuroscientists have found that a gene mutation that arose more than half a million years ago may be key to humans’ unique ability to produce and understand speech.

    image

    Researchers from MIT and several European universities have shown that the human version of a gene called Foxp2 makes it easier to transform new experiences into routine procedures. When they engineered mice to express humanized Foxp2, the mice learned to run a maze much more quickly than normal mice.

    The findings suggest that Foxp2 may help humans with a key component of learning language — transforming experiences, such as hearing the word “glass” when we are shown a glass of water, into a nearly automatic association of that word with objects that look and function like glasses, says Ann Graybiel, an MIT Institute Professor, member of MIT’s McGovern Institute for Brain Research, and a senior author of the study.

    “This really is an important brick in the wall saying that the form of the gene that allowed us to speak may have something to do with a special kind of learning, which takes us from having to make conscious associations in order to act to a nearly automatic-pilot way of acting based on the cues around us,” Graybiel says.

    Wolfgang Enard, a professor of anthropology and human genetics at Ludwig-Maximilians University in Germany, is also a senior author of the study, which appears in the Proceedings of the National Academy of Sciences this week. The paper’s lead authors are Christiane Schreiweis, a former visiting graduate student at MIT, and Ulrich Bornschein of the Max Planck Institute for Evolutionary Anthropology in Germany.

    All animal species communicate with each other, but humans have a unique ability to generate and comprehend language. Foxp2 is one of several genes that scientists believe may have contributed to the development of these linguistic skills. The gene was first identified in a group of family members who had severe difficulties in speaking and understanding speech, and who were found to carry a mutated version of the Foxp2 gene.

    In 2009, Svante Pääbo, director of the Max Planck Institute for Evolutionary Anthropology, and his team engineered mice to express the human form of the Foxp2 gene, which encodes a protein that differs from the mouse version by only two amino acids. His team found that these mice had longer dendrites — the slender extensions that neurons use to communicate with each other — in the striatum, a part of the brain implicated in habit formation. They were also better at forming new synapses, or connections between neurons.

    Pääbo, who is also an author of the new PNAS paper, and Enard enlisted Graybiel, an expert in the striatum, to help study the behavioral effects of replacing Foxp2. They found that the mice with humanized Foxp2 were better at learning to run a T-shaped maze, in which the mice must decide whether to turn left or right at a T-shaped junction, based on the texture of the maze floor, to earn a food reward.

    The first phase of this type of learning requires using declarative memory, or memory for events and places. Over time, these memory cues become embedded as habits and are encoded through procedural memory — the type of memory necessary for routine tasks, such as driving to work every day or hitting a tennis forehand after thousands of practice strokes.

    Using another type of maze called a cross-maze, Schreiweis and her MIT colleagues were able to test the mice’s ability in each of type of memory alone, as well as the interaction of the two types. They found that the mice with humanized Foxp2 performed the same as normal mice when just one type of memory was needed, but their performance was superior when the learning task required them to convert declarative memories into habitual routines. The key finding was therefore that the humanized Foxp2 gene makes it easier to turn mindful actions into behavioral routines.

    The protein produced by Foxp2 is a transcription factor, meaning that it turns other genes on and off. In this study, the researchers found that Foxp2 appears to turn on genes involved in the regulation of synaptic connections between neurons. They also found enhanced dopamine activity in a part of the striatum that is involved in forming procedures. In addition, the neurons of some striatal regions could be turned off for longer periods in response to prolonged activation — a phenomenon known as long-term depression, which is necessary for learning new tasks and forming memories.

    Together, these changes help to “tune” the brain differently to adapt it to speech and language acquisition, the researchers believe. They are now further investigating how Foxp2 may interact with other genes to produce its effects on learning and language.

    This study “provides new ways to think about the evolution of Foxp2 function in the brain,” says Genevieve Konopka, an assistant professor of neuroscience at the University of Texas Southwestern Medical Center who was not involved in the research. “It suggests that human Foxp2 facilitates learning that has been conducive for the emergence of speech and language in humans. The observed differences in dopamine levels and long-term depression in a region-specific manner are also striking and begin to provide mechanistic details of how the molecular evolution of one gene might lead to alterations in behavior.”

    The research was funded by the Nancy Lurie Marks Family Foundation, the Simons Foundation Autism Research Initiative, the National Institutes of Health, the Wellcome Trust, the Fondation pour la Recherche Médicale, and the Max Planck Society.

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  • richardmitnick 12:23 pm on September 12, 2014 Permalink | Reply
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    From M.I.T.: “Fluid mechanics suggests alternative to quantum orthodoxy” 


    MIT News

    September 12, 2014
    Larry Hardesty | MIT News Office

    New math explains dynamics of fluid systems that mimic many peculiarities of quantum mechanics.

    The central mystery of quantum mechanics is that small chunks of matter sometimes seem to behave like particles, sometimes like waves. For most of the past century, the prevailing explanation of this conundrum has been what’s called the “Copenhagen interpretation” — which holds that, in some sense, a single particle really is a wave, smeared out across the universe, that collapses into a determinate location only when observed.

    wave
    Close-ups of an experiment conducted by John Bush and his student Daniel Harris, in which a bouncing droplet of fluid was propelled across a fluid bath by waves it generated. Image: Dan Harris

    But some founders of quantum physics — notably Louis de Broglie — championed an alternative interpretation, known as “pilot-wave theory,” which posits that quantum particles are borne along on some type of wave. According to pilot-wave theory, the particles have definite trajectories, but because of the pilot wave’s influence, they still exhibit wavelike statistics.

    John Bush, a professor of applied mathematics at MIT, believes that pilot-wave theory deserves a second look. That’s because Yves Couder, Emmanuel Fort, and colleagues at the University of Paris Diderot have recently discovered a macroscopic pilot-wave system whose statistical behavior, in certain circumstances, recalls that of quantum systems.

    Couder and Fort’s system consists of a bath of fluid vibrating at a rate just below the threshold at which waves would start to form on its surface. A droplet of the same fluid is released above the bath; where it strikes the surface, it causes waves to radiate outward. The droplet then begins moving across the bath, propelled by the very waves it creates.

    “This system is undoubtedly quantitatively different from quantum mechanics,” Bush says. “It’s also qualitatively different: There are some features of quantum mechanics that we can’t capture, some features of this system that we know aren’t present in quantum mechanics. But are they philosophically distinct?”

    Tracking trajectories

    Bush believes that the Copenhagen interpretation sidesteps the technical challenge of calculating particles’ trajectories by denying that they exist. “The key question is whether a real quantum dynamics, of the general form suggested by de Broglie and the walking drops, might underlie quantum statistics,” he says. “While undoubtedly complex, it would replace the philosophical vagaries of quantum mechanics with a concrete dynamical theory.”

    Last year, Bush and one of his students — Jan Molacek, now at the Max Planck Institute for Dynamics and Self-Organization — did for their system what the quantum pioneers couldn’t do for theirs: They derived an equation relating the dynamics of the pilot waves to the particles’ trajectories.

    In their work, Bush and Molacek had two advantages over the quantum pioneers, Bush says. First, in the fluidic system, both the bouncing droplet and its guiding wave are plainly visible. If the droplet passes through a slit in a barrier — as it does in the re-creation of a canonical quantum experiment — the researchers can accurately determine its location. The only way to perform a measurement on an atomic-scale particle is to strike it with another particle, which changes its velocity.

    The second advantage is the relatively recent development of chaos theory. Pioneered by MIT’s Edward Lorenz in the 1960s, chaos theory holds that many macroscopic physical systems are so sensitive to initial conditions that, even though they can be described by a deterministic theory, they evolve in unpredictable ways. A weather-system model, for instance, might yield entirely different results if the wind speed at a particular location at a particular time is 10.01 mph or 10.02 mph.

    The fluidic pilot-wave system is also chaotic. It’s impossible to measure a bouncing droplet’s position accurately enough to predict its trajectory very far into the future. But in a recent series of papers, Bush, MIT professor of applied mathematics Ruben Rosales, and graduate students Anand Oza and Dan Harris applied their pilot-wave theory to show how chaotic pilot-wave dynamics leads to the quantumlike statistics observed in their experiments.

    What’s real?

    In a review article appearing in the Annual Review of Fluid Mechanics, Bush explores the connection between Couder’s fluidic system and the quantum pilot-wave theories proposed by de Broglie and others.

    The Copenhagen interpretation is essentially the assertion that in the quantum realm, there is no description deeper than the statistical one. When a measurement is made on a quantum particle, and the wave form collapses, the determinate state that the particle assumes is totally random. According to the Copenhagen interpretation, the statistics don’t just describe the reality; they are the reality.

    But despite the ascendancy of the Copenhagen interpretation, the intuition that physical objects, no matter how small, can be in only one location at a time has been difficult for physicists to shake. Albert Einstein, who famously doubted that God plays dice with the universe, worked for a time on what he called a “ghost wave” theory of quantum mechanics, thought to be an elaboration of de Broglie’s theory. In his 1976 Nobel Prize lecture, Murray Gell-Mann declared that Niels Bohr, the chief exponent of the Copenhagen interpretation, “brainwashed an entire generation of physicists into believing that the problem had been solved.” John Bell, the Irish physicist whose famous theorem is often mistakenly taken to repudiate all “hidden-variable” accounts of quantum mechanics, was, in fact, himself a proponent of pilot-wave theory. “It is a great mystery to me that it was so soundly ignored,” he said.

    Then there’s David Griffiths, a physicist whose Introduction to Quantum Mechanics is standard in the field. In that book’s afterword, Griffiths says that the Copenhagen interpretation “has stood the test of time and emerged unscathed from every experimental challenge.” Nonetheless, he concludes, “It is entirely possible that future generations will look back, from the vantage point of a more sophisticated theory, and wonder how we could have been so gullible.”

    “The work of Yves Couder and the related work of John Bush … provides the possibility of understanding previously incomprehensible quantum phenomena, involving ‘wave-particle duality,’ in purely classical terms,” says Keith Moffatt, a professor emeritus of mathematical physics at Cambridge University. “I think the work is brilliant, one of the most exciting developments in fluid mechanics of the current century.”

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  • richardmitnick 12:02 pm on September 12, 2014 Permalink | Reply
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    From M.I.T.: “Wrinkles in time” 


    MIT News

    September 12, 2014
    Jennifer Chu | MIT News Office

    Take a walk along any sandy shoreline, and you’re bound to see a rippled pattern along the seafloor, formed by the ebb and flow of the ocean’s waves.

    wrinkle
    An example of fossilized wrinkles taken at the Upper Cambrian Big Cove Member of the Petit Jardin Formation, near Marches Point on the Port au Port Peninsula in western Newfoundland. Photo: S. Pruss

    Geologists have long observed similar impressions — in miniature — embedded within ancient rock. These tiny, millimeter-wide wrinkles have puzzled scientists for decades: They don’t appear in any modern environment, but seem to be abundant much earlier in Earth’s history, particularly following mass extinctions.

    Now MIT researchers have identified a mechanism by which such ancient wrinkles may have formed. Based on this mechanism, they posit that such fossilized features may be a vestige of microbial presence — in other words, where there are wrinkles, there must have been life.

    “You have about 3 billion years of Earth’s history where everything was microbial. The wrinkle structures were present, but don’t seem to have been all that common,” says Tanja Bosak, the Alfred Henry and Jean Morrison Hayes Career Development Associate Professor in MIT’s Department of Earth, Atmospheric and Planetary Sciences. “But it seems they become really abundant at the time when early animals were around. Knowing the mechanism of these features gives us a better sense of the environmental pressures these early animals were experiencing.”

    Bosak and her colleagues have published their study, led by postdoc Giulio Mariotti, in the journal Nature Geoscience.

    Sedimentary footprints

    Ancient sedimentary wrinkles can be found in rocks up to 575 million years old — from a time when the earliest animals may have arisen — in places such as Australia, Africa, and Canada.

    “Some of them look like wave ripples, and others look like raindrop impressions,” Mariotti says. “They’re shapes that remain in the sediment, like the footprint of a dinosaur.”

    Researchers have put forth multiple theories for how these shapes may have arisen. Some believe that ocean waves may have created such patterns, while others think the answer may lie in ancient sea foam.

    But the prevailing theory involves the presence of microbes: In a post-extinction world, microbial mats likely took over the seafloor in wide, leathery patches that were tough enough to withstand the overlying flow. As these mats were destroyed, they left small, lightweight microbial aggregates that shifted the underlying sand, creating wavelike patterns that were later preserved in sediment.

    A fragmentary sweet spot

    To test this last theory, Mariotti attempted to recreate the wrinkled patterns by growing microbial mats in custom-built wave tanks, partially filled with sand. To track his progress, he set up a camera to take time-lapse images of the tank. His initial results were successful — although, he admits, accidental.

    “I reproduced something that looked like wrinkle structures, although at first it wasn’t on purpose,” Mariotti says.

    In his first attempts to seed a tank with microbes, Mariotti obtained fragments of microbial mats from another wave tank in which microbes were growing at a moderate rate. After a few days, he spotted tiny, millimeter-wide ripples in the sand. Looking back at the time-lapse images, he discovered the mechanism: Fragments of microbial mats were rolling along the surface and, within a few hours, rearranging sediments to create wavelike patterns in the sand.

    Mariotti followed up on the observation with more controlled experiments with various wave conditions and microbial fragments, confirming that fragments, and not whole microbes, were forming the wrinkled features in the sediment.

    The results led the group to raise another question: What might have created such microbial fragments? Bosak says the likely answer is the early appearance of small animals, which may have grazed on microbial mats, ripping them into fragments in the process.

    “What we’re suggesting is that there may be some sort of sweet spot: You can’t have too many animals feeding, because then you lose microbial mats completely, but you need enough to produce these fragments,” Bosak says. “And that sweet spot could occur after a large marine extinction event.”

    Mariotti says the mechanism he’s identified may shed light on the environmental conditions early animals faced as they tried to gain a foothold following an extinction event. For example, early animals may have thrived in protected environments such as shallow lagoons, where microbial fragments might best create wrinkled patterns.

    “You need an environment where there’s not much energy, but still some wave motion, and close enough to the photic zone where you have light, so that microbial mats can grow,” Mariotti says. “Our finding may change how we see early animals.”

    David Bottjer, a professor of earth sciences at the University of Southern California, says knowing the mechanism by which these wrinkle structures formed is important not just for understanding life on Earth, but life on other planets as well.

    “It has been suggested that if a Martian rover was scanning sedimentary rocks that had been deposited underwater, and it saw wrinkle structures, that this could mean that there was microbial life present when the rocks were deposited,” says Bottjer, who was not involved in the work. “This study provides experimental evidence that, indeed, microbial fragments derived from microbial mats would be necessary to produce wrinkle structures. So, as a ‘biomarker’ indicating that microbial life would have existed on Mars, this strengthens the case for wrinkle structures, if they are found.”

    This research was partially supported by NASA and the National Science Foundation.

    See the full article, with video, here.

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  • richardmitnick 7:47 pm on August 18, 2014 Permalink | Reply
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    From M.I.T.: “Engineering new bone growth” 


    MIT News

    August 18, 2014
    Anne Trafton | MIT News Office

    Coated tissue scaffolds help the body grow new bone to repair injuries or congenital defects.

    MIT chemical engineers have devised a new implantable tissue scaffold coated with bone growth factors that are released slowly over a few weeks. When applied to bone injuries or defects, this coated scaffold induces the body to rapidly form new bone that looks and behaves just like the original tissue.

    bone
    Pictured is a scanning electron micrograph of a porous, nanostructured poly(lactic-co-glycolic acid) (PLGA) membrane. The membrane is coated with a polyelectrolyte (PEM) multilayer coating that releases growth factors to promote bone repair. Image courtesy of Nasim Hyder and Nisarg J. Shah

    This type of coated scaffold could offer a dramatic improvement over the current standard for treating bone injuries, which involves transplanting bone from another part of the patient’s body — a painful process that does not always supply enough bone. Patients with severe bone injuries, such as soldiers wounded in battle; people who suffer from congenital bone defects, such as craniomaxillofacial disorders; and patients in need of bone augmentation prior to insertion of dental implants could benefit from the new tissue scaffold, the researchers say.

    “It’s been a truly challenging medical problem, and we have tried to provide one way to address that problem,” says Nisarg Shah, a recent PhD recipient and lead author of the paper, which appears in the Proceedings of the National Academy of Sciences this week.

    Paula Hammond, the David H. Koch Professor in Engineering and a member of MIT’s Koch Institute for Integrative Cancer Research and Department of Chemical Engineering, is the paper’s senior author. Other authors are postdocs Nasim Hyder and Mohiuddin Quadir, graduate student Noémie-Manuelle Dorval Courchesne, Howard Seeherman of Restituo, Myron Nevins of the Harvard School of Dental Medicine, and Myron Spector of Brigham and Women’s Hospital.

    Stimulating bone growth

    Two of the most important bone growth factors are platelet-derived growth factor (PDGF) and bone morphogenetic protein 2 (BMP-2). As part of the natural wound-healing cascade, PDGF is one of the first factors released immediately following a bone injury, such as a fracture. After PDGF appears, other factors, including BMP-2, help to create the right environment for bone regeneration by recruiting cells that can produce bone and forming a supportive structure, including blood vessels.

    Efforts to treat bone injury with these growth factors have been hindered by the inability to effectively deliver them in a controlled manner. When very large quantities of growth factors are delivered too quickly, they are rapidly cleared from the treatment site — so they have reduced impact on tissue repair, and can also induce unwanted side effects.

    “You want the growth factor to be released very slowly and with nanogram or microgram quantities, not milligram quantities,” Hammond says. “You want to recruit these native adult stem cells we have in our bone marrow to go to the site of injury and then generate bone around the scaffold, and you want to generate a vascular system to go with it.”

    This process takes time, so ideally the growth factors would be released slowly over several days or weeks. To achieve this, the MIT team created a very thin, porous scaffold sheet coated with layers of PDGF and BMP. Using a technique called layer-by-layer assembly, they first coated the sheet with about 40 layers of BMP-2; on top of that are another 40 layers of PDGF. This allowed PDGF to be released more quickly, along with a more sustained BMP-2 release, mimicking aspects of natural healing.

    “This is a major advantage for tissue engineering for bones because the release of the signaling proteins has to be slow and it has to be scheduled,” says Nicholas Kotov, a professor of chemical engineering at the University of Michigan who was not part of the research team.

    The scaffold sheet is about 0.1 millimeter thick; once the growth-factor coatings are applied, scaffolds can be cut from the sheet on demand, and in the appropriate size for implantation into a bone injury or defect.

    Effective repair

    The researchers tested the scaffold in rats with a skull defect large enough — 8 millimeters in diameter — that it could not heal on its own. After the scaffold was implanted, growth factors were released at different rates. PDGF, released during the first few days after implantation, helped initiate the wound-healing cascade and mobilize different precursor cells to the site of the wound. These cells are responsible for forming new tissue, including blood vessels, supportive vascular structures, and bone.

    BMP, released more slowly, then induced some of these immature cells to become osteoblasts, which produce bone. When both growth factors were used together, these cells generated a layer of bone, as soon as two weeks after surgery, that was indistinguishable from natural bone in its appearance and mechanical properties, the researchers say.

    “Using this combination allows us to not only have accelerated proliferation first, but also facilitates laying down some vascular tissue, which provides a route for both the stem cells and the precursor osteoblasts and other players to get in and do their jobs. You end up with a very uniform healed system,” Hammond says.

    Another advantage of this approach is that the scaffold is biodegradable and breaks down inside the body within a few weeks. The scaffold material, a polymer called PLGA, is widely used in medical treatment and can be tuned to disintegrate at a specific rate so the researchers can design it to last only as long as needed.

    Hammond’s team has filed a patent based on this work and now aims to begin testing the system in larger animals in hopes of eventually moving it into clinical trials.

    This study was funded by the National Institutes of Health.

    See the full article here.

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  • richardmitnick 7:27 am on May 1, 2014 Permalink | Reply
    Tags: , , , MIT News   

    From M.I.T.: “A “wimpy” dwarf fossil galaxy reveals new facts about early universe” 


    M.I.T.

    May 1, 2014
    Peter Dizikes | MIT News Office

    Out on the edge of the universe, 75,000 light years from us, a galaxy known as Segue 1 has some unusual properties: It is the faintest galaxy ever detected. It is very small, containing only about 1,000 stars. And it has a rare chemical composition, with vanishingly small amounts of metallic elements present.

    Now a team of scientists, including an MIT astronomer, has analyzed that chemical composition and come away with new insights into the evolution of galaxies in the early stages of our universe — or, in this case, into a striking lack of evolution in Segue 1. Commonly, stars form from gas clouds and then burn up as supernova explosions after about a billion years, spewing more of the elements that are the basis for a new generation of star formation.

    Not Segue 1: In contrast to all other galaxies, as the new analysis shows, it appears that Segue 1’s process of star formation halted at what would normally be an early stage of a galaxy’s development.

    “It’s chemically quite primitive,” says Anna Frebel, an assistant professor of physics at MIT, and the lead author of a new paper detailing the new findings about Segue 1. “This indicates the galaxy never made that many stars in the first place. It is really wimpy. This galaxy tried to become a big galaxy, but it failed.”

    But precisely because it has stayed in the same state, Segue 1 offers valuable information about the conditions of the universe in its early phases after the Big Bang.

    “It tells us how galaxies get started,” Frebel says. “It’s really adding another dimension to stellar archaeology, where we look back in time to study the era of the first star and first galaxy formation.”

    Metal-poor stars: a telltale sign

    The paper, Segue 1: An Unevolved Fossil Galaxy from the Early Universe, has just been published by Astrophysical Journal. Along with Frebel, the co-authors of the paper are Joshua D. Simon, an astronomer with the Observatories of the Carnegie Institution, in Pasadena, Calif., and Evan N. Kirby, an astronomer at the University of California at Irvine.

    The analysis uses new data taken by the Magellan telescopes in Chile, as well as data from the Keck Observatory in Hawaii, pertaining to six red giant stars in Segue 1, the brightest ones in that galaxy. The astronomers are able to determine which elements are present in the stars because each element has a unique signature that becomes detectable in the telescope data.

    magellan Telescopes
    Magellan Telescopes

    Keck Observatory
    Keck twin 10m telescopes

    In particular, Segue 1 has stars that are distinctively poor in metal content. All of the elements in Segue 1 that are heavier than helium appear to have derived either from just one supernova explosion, or perhaps a few such explosions, which occurred relatively soon after the galaxy’s formation. Then Segue 1 effectively shut down, in evolutionary terms, because it lost its gas due to the explosions, and stopped making new stars.

    “It just didn’t have enough gas, and couldn’t collect enough gas to grow bigger and make stars, and as a consequence of that, make more of the heavy elements,” Frebel says. Indeed, a run-of-the-mill galaxy will often contain 1 million stars; Segue 1 contains only about 1,000.

    The astronomers also found telling evidence in the lack of so-called “neutron-capture elements” — those found in the bottom half of the periodic table, which are created in intermediate-mass stars. But in Segue 1, Frebel notes, “The neutron-capture elements in this galaxy are the lowest levels ever found.” This, again, indicates a lack of repeated star formation.

    Indeed, Segue 1’s static chemical makeup even sets it apart from other small galaxies that astronomers have found and analyzed.

    “It is very different than these other regular dwarf-type galaxies that had full chemical evolution,” Frebel says. “Those are just mini-galaxies, whereas [Segue 1 is] truncated. It doesn’t show much evolution and just sits there.”

    “We would like to find more”

    Dwarf galaxies, astronomical modeling has found, appear to form building blocks for larger galaxies such as the Milky Way. The chemical analysis of Segue 1 sheds new light on the nature of those building blocks, as Frebel notes.

    Indeed, other astronomers suggest that the study of galaxies such as Segue 1 is a vital part of progress in the field. Volker Bromm, a professor of astronomy at the University of Texas, says the new paper is “very nice and important,” and “substantiates the idea” that analyzing faint dwarf galaxies produces new insight into the universe’s development.

    As Bromm points out, when it comes to the chemical composition of early stars, any search for clues among stars closer to us in the Milky Way can be problematic; most such stars have had “a very complex assembly and enrichment history, where many generations of supernovae contributed to the abundance patterns [of elements] seen in those stars.” Dwarf galaxy stars do not come with that problem.

    The findings on Segue 1 also indicate that there may be a greater diversity of evolutionary pathways among galaxies in the early universe than had been thought. However, because it is only one example, Frebel is reluctant to make broad assertions.

    “We would really need to find more of these systems,” she notes. “Or, if we never find another one [like Segue 1], it would tell us how rare it is that galaxies fail in their evolution. We just don’t know at this stage because this is the first of its kind.”

    Frebel’s work often focuses on analyzing the chemical composition of unusual stars closer to us. However, she says she would like to continue this kind of analysis for any other galaxies like Segue 1 that astronomers may find. That process could take a while; she acknowledges that any such future discoveries will require “patience, and a little luck.”

    See the full article here.


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  • richardmitnick 8:08 am on March 30, 2014 Permalink | Reply
    Tags: , , MIT News   

    From M.I.T.: “Researchers find that going with the flow makes bacteria stick” 

    February 23, 2014
    David L. Chandler, MIT News Office

    In surprising new discovery, scientists show that microbes are more likely to adhere to tube walls when water is moving.

    bactria

    In a surprising new finding, researchers have discovered that bacterial movement is impeded in flowing water, enhancing the likelihood that the microbes will attach to surfaces. The new work could have implications for the study of marine ecosystems, and for our understanding of how infections take hold in medical devices.

    The findings, the result of microscopic analysis of bacteria inside microfluidic devices, were made by MIT postdoc Roberto Rusconi, former MIT postdoc Jeffrey Guasto (now an assistant professor of mechanical engineering at Tufts University), and Roman Stocker, an associate professor of civil and environmental engineering at MIT. Their results are published in the journal Nature Physics.

    The study, which combined experimental observations with mathematical modeling, showed that the flow of liquid can have two significant effects on microbes: “It quenches the ability of microbes to chase food,” Stocker says, “and it helps microbes find surfaces.”

    That second finding could be particularly beneficial: Stocker says in some cases, that phenomenon could lead to new approaches to tuning flow rates to prevent fouling of surfaces by microbes — potentially averting everything from bacteria getting a toehold on medical equipment to biofilms causing drag on ship hulls.

    The effect of flowing water on bacterial swimming was “a complete surprise,” Stocker says.

    “My own earlier predictions of what would happen when microbes swim in flowing water had been: ‘Nothing too interesting,’” he adds. “It was only when Roberto and Jeff did the experiments that we found this very strong and robust phenomenon.”

    Even though most microorganisms live in flowing liquid, most studies of their behavior ignore flow, Stocker explains. The new findings show, he says, that “any study of microbes suspended in a liquid should not ignore that the motion of that liquid could have important repercussions on the microbes.”

    The novelty of this result owes partly to the divisions of academic specialties, and partly to advances in technology, Stocker says. “Microbiologists have rarely taken into account fluid flow as an ecological parameter, whereas physicists have just recently started to pay attention to microbes,” he says, adding: “The ability to directly watch microbes under the controlled flow conditions afforded by microfluidic technology — which is only about 15 years old — has made all the difference in allowing us to discover and understand this effect of flow on microbes.”

    The team found that swimming bacteria cluster in the “high shear zones” in a flow — the regions where the speed of the fluid changes most abruptly. Such high shear zones occur in most types of flows, and in many bacterial habitats. One prominent location is near the walls of tubes, where the result is a strong enhancement of the bacteria’s tendency to adhere to those walls and form biofilms.

    But this effect varies greatly depending on the speed of the flow, opening the possibility that the rate of biofilm formation can be tweaked by increasing or decreasing flow rates.

    Guasto says the new understanding could help in the design of medical equipment to reduce such infections: Since the phenomenon peaks at particular rates of shear, he says, “Our results might suggest additional design criteria for biomedical devices, which should operate outside this range of shear rates, when possible — either faster or slower.”

    Biofilms are found everywhere,” Rusconi says, adding that the majority of bacteria spend significant fractions of their lives adhering to surfaces. “They cause major problems in industrial settings,” such as by clogging pipes or reducing the efficiency of heat exchangers. Their adherence is also a major health issue: Bacteria concentrated in biofilms are up to 1,000 times more resistant to antibiotics than those suspended in liquid.

    The concentration of microbes in the shear zones is an effect that only happens with those that can control their movements. Nonliving particles of similar size and shape show no such effect, the team found, nor do nonmotile bacteria that are swept along passively by the water. “Without motility, bacteria are distributed everywhere and there is no preferential accumulation,” Rusconi says.

    The new findings could also be important for studies of microbial marine ecosystems, by affecting how bacteria move in search of nutrients when one accounts for the ubiquitous currents and turbulence, Stocker says. Though they only studied two types of bacteria, the researchers predict in their paper that “this phenomenon should apply very broadly to many different motile microbes.”

    In fact, the phenomenon has no inherent size limit, and could apply to a wide range of organisms, Guasto says. “There’s really nothing special about bacteria compared to many other swimming cells in this respect,” he says. “This phenomenon could easily apply to a wide range of plankton and sperm cells as well.”

    Howard A. Stone, a professor of mechanical and aerospace engineering at Princeton University, who was not involved in this research, calls this a “very interesting paper” and says “the observation of shear-induced trapping, which can impact the propensity for bacterial attachment on surfaces, is an important observation and idea, owing to the major importance of bacterial biofilms.”

    See the full article here.


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  • richardmitnick 7:52 am on October 4, 2013 Permalink | Reply
    Tags: , , MIT News,   

    From M.I.T.: “New kind of microscope uses neutrons” 

    October 4, 2013
    David L. Chandler, MIT News Office

    Researchers at MIT, working with partners at NASA, have developed a new concept for a microscope that would use neutrons — subatomic particles with no electrical charge — instead of beams of light or electrons to create high-resolution images.

    micro
    No image credit

    Among other features, neutron-based instruments have the ability to probe inside metal objects — such as fuel cells, batteries, and engines, even when in use — to learn details of their internal structure. Neutron instruments are also uniquely sensitive to magnetic properties and to lighter elements that are important in biological materials.

    The new concept has been outlined in a series of research papers this year, including one published this week in Nature Communications by MIT postdoc Dazhi Liu, research scientist Boris Khaykovich, professor David Moncton, and four others.

    See the full article here.


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